hmm Personaly I like it, it helps me to tell wether I should stay on a bit more, cause someone is posting a reply in a thread I was waiting for
or to see wether or not that person is doing something else
it's also useful to see wether or not someone is idle or not, can be annoying when you send a PM to someone who is online and he or she takes a few hours to PM ya back, but if you can see that he was last active about an hour ago, you see that he's idle