I don't speculate in the bitcoin market anymore, because the the legal/regulatory environment is too chaotic for my taste. But I made decent money earlier in the year, mostly through arbitrage opportunities through the different exchanges. Not that I recommend it to anyone; I'm just saying that there could still be money to be made in the short term for those with a high tolerance for risk. And that is why many of us are here, right? To make money on short-term trades? In that sense, I see BTC as just another currency - albeit one with ridiculous volatility.
There is a demand for this kind of currency out there - criminals, libertarians, geeks, disillusioned gold-bugs. I don't know if BTC itself will last, but I think crypotcurrencies will be with us for a long time, and will prove to be highly disruptive to the banking industry.