Ross, the Spammers are generally not real people. They use an automated program called "Xrumer" which is sold as a "Search Engine Optimization" (SEO) tool. Unsuspecting (or morally deficient) companies will buy this hoping to get a boost in their search engine rankings and/or traffic. It uses a database of throw-away (or hacked) email accounts and proxy servers/hacked PCs worldwide to generate user accounts on forums. Most accounts won't actually post anything - but they will have a link in the signature or elsewhere in order for the search engines to pick them up. The ones posting are generally trying to generate click-throughs because they are ad supported. There must have been a recent upgrade (or someone forgot to code a filter into the program) because activity has spiked massively in the last couple of weeks. I use a custom "block list" of servers worldwide (servers in a colocation should never be generating web traffic unless they are spiders/crawlers) which typically weeds out nearly everything but the zombie PCs. I do this at the network level so the forum software never even sees them. For individual accounts I check them against stopforumspam.com and projecthoneypot.org. I have recently found 2 mods for SMF that will automatically verify new accounts against these databases. Saves a LOT of time! Even better, they don't impact "real" users at all.
Troy