How To Build a Naive Bayes Classifier
http://bionicspirit.com/blog/2012/02/09/howto-build-naive-bayes-classifier.html
Some use-cases for building a classifier:
Spam detection, for example you could build your own Askimet API; Automatic assignment of categories to a set of items; Automatic detection of the primary language (e.g. Google Translate); Sentiment analysis, which in simple terms refers to discovering if an opinion is about love or hate about a certain topic;