I think it's main purpose is for use as a currency and so far, that's the best use I've come up with.  The nice thing about using BTC as currency is that quite a few places offer a discount for using it.  It has many advantages in an online world.  I don't think it's a replacement currency though and wouldn't use it for all purchases all the time.

I'd love to treat BTC as an investment but the market is still relatively new and the price is highly volatile -- the "true value" is anybody's guess.  Major price fluctuations are the main reason I don't see it as a typical buy-and-hold investment, but there's a lot of fun with short-term trades.

Investment or currency, at least BTC is being used and the use seems to be growing which should make all of us happy.