The actual bump posts aren't annoying, as it does increase the number of people who read a thread. Example: someone asks a question late at night, and only gets like 2 replies. If the OP then bumps the thread during the day (when all of us slackers are avoiding doing any sort of real work to earn our paychecks), he'll get more replies.
The ones that annoy me are the retarded "tag" posts *cough*BAFF*cough*. Why people do it to dead threads is beyond me, as it's not like it'll show up in their unreads (unless some other annoying person tags it too). Tags work on an active thread, but if you're not going to make any sort of useful comment at all on one that's been dead and buried, it's a waste of time and doesn't further any discussion.