user1069: I've read the introduction to bitcoins. But the main question remains: what reasons could push me to buy bitcoins today?

user323: 
Bitcoins are currently semi-low in value, if you think they will go up in value, they are a good investment.

One can expect their value to rise due to the bock reward being halved in about a year.

If you suspect your local currency or banks available to you to be unstable (say, you live in Greece and you want to stay away from the greek banks), Bitcoins might be a more preferable solution to standard banking. Nobody can steal your coins.
If you like new tech gadgets, getting to know Bitcoins as a possible new "thing" on the Internet might be up your alley.
If you are performing a lot of online money transfers, especially between countries, operating in Bitcoins can save you some money.
If you are dealing with people that already accept Bitcoins, it might be a necessity for you.

But in the end, there is no real reason to be "pushed" into using Bitcoins (at least currently). If you organically find Bitcoins to be a better solution for some problems you encounter, you can try them as an alternative. Other than that it's still a new technology for enthusiasts, computer-savvy people and speculators. If you don't find any reasons to buy them currently, chances are it might take some time before new reasons appear.

user1072: If you are a student from China, studying in the UK (say) - you can buy bitcoins on btcchina.com directly from your Chinese bank account, send them to Intersango.com and sell them for GBP, and transfer them to your UK bank account. 
You can avoid having to send thousands of pounds to a British bank account to cover your expected expenses and instead just convert your money as and when you need it.

user153: For speculation, you would buy when the price is low in anticipation that the price will rise in the future.
There are some signs that the currency is seeing wider use and has greater potential in the future.  For instance:
 - http://blockchain.info/charts/n-transactions
Concluding that that growth means that a bitcoin will be worth $4 or $2 or $32 by any certain date is more or less speculation though.  
As far as why you might want to buy bitcoins today?
How about to participate in an online lottery where the jackpot payout return is 99% of the total wagers.  Beats the heck out of doing a scratch-off at the gas station.  Tickets are about $1 each.
 - http://www.bitlotto.com
How about for the novelty.  Have you ever bought a quart of pure maple syrup direct from the farm?
 - https://bitcointalk.org/index.php?topic=55594.0
or Alpaca socks?
 - http://www.grasshillalpacas.com/alpacaproductsforbitcoinoffer.html
or a Blue Canary Night Light:
 - http://bluecanarynightlight.com
How about to prove your brilliance?  Bets of Bitcoin is a predictions market.
 - http://betsofbitco.in
Maybe you want to purchase something and would rather that purchase not show on your credit card bill.  Or not.
Or maybe you want to make a purchase from someone on Craigslist and don't know if you can trust that they'll ship your order.  There are escrow services (with dispute resolution) available using bitcoins (compare BTCrow's 1% to escrow.com's $25 minimum fee):
 - http://www.btcrow.com
Maybe you want to send a few bucks to someone in another country as an expression of appreciation.  Bitcoin transfers are nearly instant and know no borders.

user117: To participate in a disruptive technology
Many of the other answers are covering the investment angle, but also consider that Bitcoin is a disruptive technology. Bitcoin allows an individual the kind of control over their money which has never been available before in all of history. 
This is a very big deal. It is now possible to send any amount of money, to anyone, anywhere in the world, anonymously (if you're very careful) in moments. This was not possible before now for a multitude of reasons:

governments restricting destinations / amounts
banks not having a presence in some regions
excessive fees (particularly for small amounts)
unreliability of some postal services

All of the above may or may not concern you, but they do affect the lives of many. By offering an alternative Bitcoin can potentially bring about a societal change in the same way that mobile phones and email have. Already the idea of sending someone some small change, in bitcoins, as a reward for their creative efforts has become commonplace to me. 
The knock-on effect of this is to encourage that author or artist to produce more, and the world becomes enriched. In volume, those bitcoins can free them from a tedious day job and allow them to pursue their dream. 
Surely, that's worth a bitcoin.

1069: <p>I've read the introduction to bitcoins. But the main question remains: what reasons could push me to buy bitcoins today?</p>
 323: <ul>
<li>Bitcoins are currently semi-low in value, if you think they will go up in value, they are a good investment.
<ul>
<li>One can expect their value to rise due to the bock reward being halved in about a year.</li>
</ul></li>
<li>If you suspect your local currency or banks available to you to be unstable (say, you live in Greece and you want to stay away from the greek banks), Bitcoins might be a more preferable solution to standard banking. Nobody can steal your coins.</li>
<li>If you like new tech gadgets, getting to know Bitcoins as a possible new "thing" on the Internet might be up your alley.</li>
<li>If you are performing a lot of online money transfers, especially between countries, operating in Bitcoins can save you some money.</li>
<li>If you are dealing with people that already accept Bitcoins, it might be a necessity for you.</li>
</ul>

<p>But in the end, there is no real reason to be "pushed" into using Bitcoins (at least currently). If you organically find Bitcoins to be a better solution for some problems you encounter, you can try them as an alternative. Other than that it's still a new technology for enthusiasts, computer-savvy people and speculators. If you don't find any reasons to buy them currently, chances are it might take some time before new reasons appear.</p>
 1072: <p>If you are a student from China, studying in the UK (say) - you can buy bitcoins on btcchina.com directly from your Chinese bank account, send them to Intersango.com and sell them for GBP, and transfer them to your UK bank account. 
You can avoid having to send thousands of pounds to a British bank account to cover your expected expenses and instead just convert your money as and when you need it.</p>
 153: <p>For speculation, you would buy when the price is low in anticipation that the price will rise in the future.</p>

<p>There are some signs that the currency is seeing wider use and has greater potential in the future.  For instance:
 - <a href="http://blockchain.info/charts/n-transactions">http://blockchain.info/charts/n-transactions</a></p>

<p>Concluding that that growth means that a bitcoin will be worth $4 or $2 or $32 by any certain date is more or less speculation though.  </p>

<p>As far as why you might want to buy bitcoins today?</p>

<p>How about to participate in an online lottery where the jackpot payout return is 99% of the total wagers.  Beats the heck out of doing a scratch-off at the gas station.  Tickets are about $1 each.
 - <a href="http://www.bitlotto.com">http://www.bitlotto.com</a></p>

<p>How about for the novelty.  Have you ever bought a quart of pure maple syrup direct from the farm?
 - <a href="https://bitcointalk.org/index.php?topic=55594.0">https://bitcointalk.org/index.php?topic=55594.0</a>
or Alpaca socks?
 - <a href="http://www.grasshillalpacas.com/alpacaproductsforbitcoinoffer.html">http://www.grasshillalpacas.com/alpacaproductsforbitcoinoffer.html</a>
or a Blue Canary Night Light:
 - <a href="http://bluecanarynightlight.com">http://bluecanarynightlight.com</a></p>

<p>How about to prove your brilliance?  Bets of Bitcoin is a predictions market.
 - <a href="http://betsofbitco.in">http://betsofbitco.in</a></p>

<p>Maybe you want to purchase something and would rather that purchase not show on your credit card bill.  Or not.</p>

<p>Or maybe you want to make a purchase from someone on Craigslist and don't know if you can trust that they'll ship your order.  There are escrow services (with dispute resolution) available using bitcoins (compare BTCrow's 1% to escrow.com's $25 minimum fee):
 - <a href="http://www.btcrow.com">http://www.btcrow.com</a></p>

<p>Maybe you want to send a few bucks to someone in another country as an expression of appreciation.  Bitcoin transfers are nearly instant and know no borders.</p>
 117: <p><strong>To participate in a disruptive technology</strong></p>

<p>Many of the other answers are covering the investment angle, but also consider that Bitcoin is a disruptive technology. Bitcoin allows an individual the kind of control over their money which has never been available before in all of history. </p>

<p>This is a very big deal. It is now possible to send any amount of money, to anyone, anywhere in the world, anonymously (if you're very careful) in moments. This was not possible before now for a multitude of reasons:</p>

<ul>
<li>governments restricting destinations / amounts</li>
<li>banks not having a presence in some regions</li>
<li>excessive fees (particularly for small amounts)</li>
<li>unreliability of some postal services</li>
</ul>

<p>All of the above may or may not concern you, but they do affect the lives of many. By offering an alternative Bitcoin can potentially bring about a societal change in the same way that mobile phones and email have. Already the idea of sending someone some small change, in bitcoins, as a reward for their creative efforts has become commonplace to me. </p>

<p>The knock-on effect of this is to encourage that author or artist to produce more, and the world becomes enriched. In volume, those bitcoins can free them from a tedious day job and allow them to pursue their dream. </p>

<p>Surely, that's worth a bitcoin.</p>
