Awesome, you should keep going! I've only seen one other sentiment analysis of bitcoin so far, boring market!
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=qerm.. I want to see a correlation but I only see an idea?..
Yeah, the idea is not new, what is most difficult is to fine-tune the Bayesian Classifier, you need to train your bots properly and separate the market sentiment. I bet with more time someone will come up with fine-tuned bots that predict the market with an astonishing accuracy, and in real-time...
http://glowingpython.blogspot.com.es/2013/04/real-time-twitter-analysis.html