Buffett cautious amid IPO rush Sometimes you think you've seen everything that can possibly happen when it comes to investing and finance. Then the Winklevoss twins prove you wrong, again. This time, they've suggested that Bitcoins - the virtual would-be currency - could be a national currency one day. Yes, the brothers famous for claiming they really were the brains behind the birth of Facebook (Nasdaq: FB) have decided an online payment method preferred mostly by criminals and paranoid anti-government types might one day carry the head of a sovereign on its obverse. You know, I could be wrong. But the odds of that are pretty small, with the possible exception that a rogue government might just think the idea is crazy enough to work. Yes, I'm looking at you, North Korea. But let's face it - the imprimatur of Kim Jong-un would be the exception to prove this rule. No one has ever invoked the North Korean leadership as moral authority - and that's unlikely to start any time soon. Confidence - and risk - soars The broader economic picture might be somewhat of a patchwork, but that's not stopping investors. In case you wanted proof, almost 600 US companies hit 52-week highs after the Federal Reserve's decision to hold fire on reducing quantitative easing. Still not convinced? The market in initial public offerings is hitting its straps, with Twitter, Freelancer.com and plenty of others lining up to list on the main exchanges, and the aforementioned Winklevoss twins figure this is an attractive market into which to tip a Bitcoin-based exchange traded fund. Don't get me wrong: I'm not suggesting the markets are getting to bubble territory yet but it's hard to argue that the markets aren't - at least in part - starting to lose their inhibitions. And that's when investors should start to be wary. If you're thinking I'm the guy who takes away the punchbowl just as the party gets into full swing, or the neighbour who calls the police when the music gets too loud, then I'm - at least metaphorically - guilty as charged. Everything in moderation I'm not suggesting the punch isn't good or the music enjoyable - just that the result of unbridled indulgence tends to be a pretty rough hangover. That's a day wasted in bed if you party too hard. It can be many thousands of dollars up in smoke when it comes to investing. To torture the metaphor a little further, by all means enjoy the party. Have some punch. A little can be a good thing. Just because the market is getting more expensive doesn't mean there aren't good investments to be found. There are fewer than at this time 12 and 24 months ago, but they're out there. Warren Buffett, the greatest living investor, seems to agree, telling US cable channel CNBC that US shares are "more or less fairly priced now." Foolish takeaway That said, not investing at all can be the worst form of risk. The ASX has expanded almost 30-fold in the past three decades, through wars, recessions, crashes and panics. But when speculation takes over and investors start to feel the envy of missing out on the gains others are enjoying, you know it's time to be careful. The single worst reason to buy an investment is the money other people are making. By the time everyone's talking about it, most of the gains will probably have been realised, and we're closer to the end of the party than almost everyone knows. Only in hindsight will we realise we shouldn't have had that last drink (or three), but by then it's too late. The Winklevoss twins are welcome to their Bitcoins. I wish every success to the companies floating on the stock exchange. Just remember, they're not selling because they want you to be rich, but because they want your cash. And no one in their right mind sells cheaply. Click here to request a Motley Fool free report entitled Secure Your Future with 3 Rock-Solid Dividend Stocks. Scott Phillips is a Motley Fool investment adviser. He owns shares in Berkshire Hathaway. Twitter @TMFGilla. This article contains general investment advice only (under AFSL 400691).