There's been buckets of electronic ink spilled regarding the merits and drawbacks of bitcoin as both the currency of the future and it's value as in investment. Very intelligent people have come down on both sides. A simple google search will turn up days worth of reading material from people who have thought about the problem far more deeply than anyone on this board.
At the end of the day, it's like gold. It's an unproductive asset that can be viewed as an alternative to sovereign backed currency. It's worth whatever the market says it is and the price volatility should be evidence enough that any notion of a "correct" valuation is sort of ridiculous. But unlike gold, it doesn't have a 5000yr track record as an alternative currency.
I suppose if you want to punt around in it with a 1-3% of your portfolio, there's probably little harm in it. It may act as an interesting diversifier, though the history of bitcoin is too short to make any definitive pronouncements. Just don't drink the cool-aid and think you're doing anything more than gambling.