The look and feel, as well as overall usability of the SE-sites, is awesome--I enjoy reading over here.
I think that the process to add favorite tags can be more practical: when hovering over a tag (a small window pops-up anyway with a definition and a few options to follow, et.c.), an option to mark this tag as favorite (of course for logged-in users) would simplify things.
What do you think about this?