I actuelly never used the training feature because I have no idea how it works and what impact is has.
I’d prefer a blacklist mechanism (with or without RegEx) and probably a whitelist mechanism optionally for highlighting.
Ultra-cool would be a scoring feature just like in advanced newsgroup clients back in the good old days: associate positive (upranking) and negative (downranking) integers to words and define a threshold for highlighting and hiding entries acccording to the sum of scores per item. Probably not for Jow Average but awesome control for tech-savvy users like me.
Edit: actually, I liked the idea of having a scoring mechanism as well so I wrote Scoring articles for highlighting and hiding