We could ban ips on the old UBB forums but we haven't had that ability since switching to IPB in 2004. We can request ip bans but an admin has to do it.
The spambot filter and CAPTCHA does block most ad spam but you're right that they still get through on occasion. The filter looks at the first one or two posts made by an account and if it has lots of links it's made invisible (which automatically flags it for us). Occasionally someone's first post is a bunch of screen shots and we have to re-enable it but usually it only hides the trash. For a while there we were banning ad bots a few times a week but lately it hasn't been much of a problem.