user9479: (This question applies to private wallets, stored in a local computer. Not so much for online wallets, which are supposed to always be connected to the internet) 
Let's say I have a wallet with several addresses. Somebody (maybe even myself) makes a transfer to one of my addresses. My impression is that my bitcoin client (the one managing the wallet to which the address is associated) must be running and connected to the internet in order for this transfer to be executed.
I say this because, since a wallet has real money, the bitcoins (those unique bitcoins that have been transferred) must arrive to the wallet somehow. But if my wallet is not connected, this is impossible.
So here my questions:

what happens if the wallet is not connected to the internet? Where are the bitcoins? Are they in a "bitcoin limbo" until they are transferred to my wallet? 
How is this managed from the blockchain point of view? Are transfers marked as "done" when the money has been transferred to a wallet?
is there any kind of timeout? What happens if I do not connect my client for a day / month / year / ever? Are the bitcoins lost, or is the transfer cancelled?

Maybe I am misunderstanding what an address / wallet really represents.

user46619: You can certainly receive payments without being online. But you must be online to send payments. 

I can make as many copies of my wallet as I want to, since all of them will have the same keypair, right?

It's less a matter of making copies of your wallet as it is a matter of creating new wallets and storing the same keypairs in them. You can have as many wallets as you want to bother to create, and keep in those wallets the same addresses that you are using. But many people just let their wallet(s) create a new public address for each new transaction they make. Those people may or may not bother to learn of and keep a copy of each new public address's private key. Where that is the case, to lose your wallet's password is indeed to lose your coins. Since you don't know the private keys that your wallet created for each transaction you made, you cannot withdraw any bitcoins out of those addresses. That's why backing up your wallet is so important. But if you make a point of keeping your private keys in a safe place, you have that extra margin of safety because you can always generate a public address from a private key, but never the other way around,. 

user2924: No, the transactions are weaved into the blockchain by the p2p network of miners. That's what counts. Your address is only a keypair that proves you ownership. The concept of cold storage is exactly the idea to not connect to the internet so nobody can steal your coins (or rather, the key to access your wallet).

user5406: You can receive payments without being online.
Your wallet's purpose is mainly to store your private keys which enable you to spend balances associated with corresponding addresses. The actual bitcoin balances are stored in the blockchain ("the public ledger") which is constantly being updated by the bitcoin network even when you are offline. When you open your wallet, it will catch up to the current status by validating any blocks that occurred while you were offline. The balance shown in your wallet only represents a snapshot of the latest information available to your wallet (which may lag behind if you aren't synchronized, or may be accurate, if you are currently in sync with the network).
So, Bitcoin payments will arrive just fine with you being offline, you just probably won't be aware of it until later.

9479: <p>(This question applies to private wallets, stored in a local computer. Not so much for online wallets, which are supposed to always be connected to the internet) </p>

<p>Let's say I have a wallet with several addresses. Somebody (maybe even myself) makes a transfer to one of my addresses. My impression is that my bitcoin client (the one managing the wallet to which the address is associated) must be running and connected to the internet in order for this transfer to be executed.</p>

<p>I say this because, since a wallet has <em>real money</em>, the bitcoins (those <em>unique</em> bitcoins that have been transferred) must arrive to the wallet somehow. But if my wallet is not connected, this is impossible.</p>

<p>So here my questions:</p>

<ul>
<li>what happens if the wallet is not connected to the internet? Where are the bitcoins? Are they in a "bitcoin limbo" until they are transferred to my wallet? </li>
<li>How is this managed from the <code>blockchain</code> point of view? Are transfers marked as "done" when the money has been transferred to a wallet?</li>
<li>is there any kind of timeout? What happens if I do not connect my client for a day / month / year / ever? Are the bitcoins lost, or is the transfer cancelled?</li>
</ul>

<p>Maybe I am misunderstanding what an address / wallet really represents.</p>
 46619: <p>You can certainly <em>receive</em> payments without being online. But you must be online to <em>send</em> payments. </p>

<blockquote>
  <p>I can make as many copies of my wallet as I want to, since all of them will have the same keypair, right?</p>
</blockquote>

<p>It's less a matter of making copies of your wallet as it is a matter of creating new wallets and storing the same keypairs in them. You can have as many wallets as you want to bother to create, and keep in those wallets the same addresses that you are using. But many people just let their wallet(s) create a new public address for each new transaction they make. Those people may or may not bother to learn of and keep a copy of each new <em>public</em> address's <em>private</em> key. Where that is the case, to lose your wallet's password is indeed to lose your coins. Since you don't know the private keys that your wallet created for each transaction you made, you cannot withdraw any bitcoins out of those addresses. That's why backing up your wallet is so important. But if you make a point of keeping your private keys in a safe place, you have that extra margin of safety because you can always generate a <em>public</em> address from a <em>private</em> key, but never the other way around,. </p>
 2924: <p>No, the transactions are weaved into the blockchain by the p2p network of miners. That's what counts. Your address is only a keypair that proves you ownership. The concept of cold storage is exactly the idea to not connect to the internet so nobody can steal your coins (or rather, the key to access your wallet).</p>
 5406: <p>You can receive payments without being online.</p>

<p>Your wallet's purpose is mainly to store your private keys which enable you to spend balances associated with corresponding addresses. The actual bitcoin balances are stored in the blockchain ("the public ledger") which is constantly being updated by the bitcoin network even when you are offline. When you open your wallet, it will catch up to the current status by validating any blocks that occurred while you were offline. The balance shown in your wallet only represents a snapshot of the latest information available to your wallet (which may lag behind if you aren't synchronized, or may be accurate, if you are currently in sync with the network).</p>

<p>So, Bitcoin payments will arrive just fine with you being offline, you just probably won't be aware of it until later.</p>
