TBH I don't know enough about it to have an opinion. I know it's not a good idea to throw around money on something you don't understand though.
Also: How the fuck do you even spend it OR cash it in?
Despite all the money people waste on the stock market, most reasonable people will say that the value of a stock is represented in its price. That is to say, you can almost never "beat the market" by purchasing a cheap stock and having the price shoot up later. That may happen, but on average, you will neither lose nor gain more money in the stock market than you put in, because enough people have thought about this stuff for a long enough time that, on balance, X dollars = X dollars at the end of the day, taking interest rates and whatever else into account. In other words, gambling is a bad idea.
BitCoin fanatics suggest that, in addition to being a unit of exchange, it's an asset that will gain value over time, which means that the law I just described applies to it. Along with the wholesale disappearance of Mt. Gox, I would suggest that BitCoin is eventually going to lose its value enough that the money people put in equals the money they get out- or worse, it will lose value as an investment. It's stupid to gamble on the stock market (that's why mutual funds exist), and it's stupid to play currency arbitrage with money that was invented by a bunch of internet nerds and not a responsible central bank.
There are all sorts of horror stories about complete nincompoops who have done precisely this. A couple of months ago on reddit I saw a guy who admitted to spending his sister's inheritance money gambling on BitCoin.