Two suggestions on comments/commenting on question and answers:
imo, it would look nice if a user's ID that is prefixed with @ in a comment was formatted subtly different (color? bold?) from the other text in the comment. For example: "@liao: so is not so-so" could be "@liao: so is not so-so" (no pun intended :)
when creating a comment, it would be useful (no proof, just feels "right") to ask the commenter "who" the comment is directed at.
a. "who" = user id picked from asker and other commenters on the quesion
b. in case of a comment referencing multiple commenters, point #1 may help instead?
Feel free to trample on all the above - they are just thoughts i had in the short time i've been using this site, so i had to at least put it "out