I posted about this in http://moodle.org/mod/forum/discuss.php?d=83627 because there's a related but very old bug and I'm not sure if I'm being stupid and missing something that already exists.

Bascially I think it would be great if we could monitor tags by RSS, so you can take the feed of, say, "development" and see when new users tag themselves with that term and new blog entries get tagged with that, and new courses get tagged with that etc etc