Recently, i have find some theme-ing functions that cannot be simply find by theme developer module, as that theme function only calls when you are anonymous user.

comment.module theme_comment_post_forbidden() is an example.
This function render the "Please login to post comments" to anonymous user, request them to login in order to get access to the comment form.

As theme developer do not appears when you are not admin, so when i want to theme this sentence, i spend some time to find out the function is defined in comment module, which is reasonable.

Hope this small tips helps someone.