You can always exchange your BitCoins for cash, so you're not obligated to only spend them with some other vendor that accepts them. Current price is around $130 / BitCoin, but you can trade arbitrary fractions of coins.
BitCoin is pretty cool and it will be a big deal one day. The total number of BitCoins is limited, and the design of the system automatically prevents the introduction of a flood of new BitCoins, so there will never be inflation as a result of anyone "printing BitCoins." Since the supply is limited, the price will continue to rise as it gets more and more popular. I think this is inevitable - BitCoin is still in the very early stages, and will get a whole lot more popular as it matures. The price may drop a bit in the short term, but in the long term, it stands to increase quite a bit more, as long as the governments do not step in and declare it illegal. I think it would be very difficult for a government to do that - because of how the system works, you could probably argue that a ban on BitCoins would be a violation of the 1st amendment in the US.
That said - at the moment, I think BitCoin is a bit risky and technically immature. The design of the BitCoin system itself is sound, but the sites that allow you to exchange your BitCoins for dollars are all a bit shady and of questionable quality - and if they get hacked or suffer a technical malfunction, your BitCoins can be stolen or literally lost. This is not a theoretical issue - it has happened many times already in the short history of BitCoin.
For the moment, it's a cool thing and a novelty, and in any case you should be able to exchange your BitCoins for dollars pretty easily and without much risk if someone wants to pay you with them. Make sure you charge a healthy premium for the inconvenience and the volatility, like 25% of the current exchange rate or something. Alternatively, you can just hold onto the BitCoins and gamble that the price will increase, which I think is a reasonable bet.
My prediction is in the next 2-3 years BitCoin will become a major force in international finance, and, yes, international crime. It will be really interesting to see where it leads. And for anyone concerned about "Big Brother" monitoring your transactions and your finances, it is a perfect solution.