Part of the problem is that IRC bots are meant to be a way of getting information into the IRC environment. The CB environment is the web, so there's not much reason for that. !g Foo? Why not just google it? Or, for that matter, just write Foo -- part of the reason to write a bot just gets subsumed by perlmonks itself.

That said, I still think the best metric is "don't be annoying". I don't think responding to chatter is necessarily annoying, even if you do it when not addressed directly, so long as you don't do it too much -- if your bot is in the top 10 on the CB stats, you're probably doing it too much.

If people keep thinking "didn't she just say that", it's probably talking too much...

If it starts spouting wrong answers to questions, it, er, needs a better AI.