Also, you may want to tweak the code that parses the "TWEET" tag. Right now it's case senstivie, so TWEET works, but tweet doesn't (more [a-z][A-Z] than just [a-z]). This is contrary to the way other formatting tags work (which are all, afaik, case insensitive).
And... d'oh I think I know what my problem was in those previous posts.