On one of this sites lower trafficked sister sites has a piece of software called "Spam-O-Matic (yes really), think it's been installed just a few years. The statistics to date read something like this:
79632 Spammers Denied Registration
273 Spammers Permanently Banned
341 Spammers submitted to Akismet
77362 Spammy Posts Automatically Moderated
I'll leave it at that