I also use python, though I don't use NLTK. I learned python with the NLTK book though. I knew I wanted to do this with stocks, and didn't know which language to use. I eventually had a friend show me that book so python became the language.
Certainly this field will be further explored in the coming months/years. I also did it just out of curiosity. I'm not a trader, just a webdev with some python background, but I clearly see room for profit here. I mean, you just have to look to Google trends to see that 'bitcoin interest' = 'market response'.
http://www.google.com/trends/explore#q=bitcoin&date=today%2012-m&cmpt=q
Haha, yep. Some of the best indicators are the simplest. That one is good, I also measure chatter amount on Twitter and Stocktwits on bitcoin.
It doesn't seem to matter too much what the chatter is, barring very bad events like Gox. If there's a lot of discussion price is going up, at least so far. Eventually that will change once it is mainstream. For now, all press is good press, seems to be spreading curiosity for bitcoin. I know that's what brought me in.