If you use the Biggest Bot List long enough and get visited by enough bots, your MySQL database will commit suicide due to the massive filling of the spider logs.
One such result I've read of this event can be seen in the following error code:
IPB WARNING [2] preg_match() [function.preg-match]: Compilation failed: repeated subpattern is too long at offset 30938 (Line: 187 of /sources/classes/class_session.php)
IPB 2.2 has a task to already prune the spider logs, but 2.1 and 2.0 need some help
For IPB 2.1, go over to IPS Beyond and get the task, and users of 2.0 should go here.