I hate the buggers, the way it went for me was a single comment on one post, evidently a test, which I deleted when I noticed it. That single post then got bombarded, absolutely bonkers, so I enabled askimet and logged well over 2000 spam comments in a couple of days. Although askimet was catching them all at the time I figured an extra level of protection was required, hence finding bad behaviour.
The only caveat with bad behaviour is that by default it puts a little bit of text in the footer of your blog, I considered that a fair price for the benefits. All it says is
"Bad Behavior has blocked 33 access attempts in the last 7 days.", clearly changed for the number of attempts it has actually encountered.