The places I used to hang out with PHPBB or similar forums never really had problems with bots. And I'm at least pretty sure they were popular places. Penny-Arcade, Something Awful, NewGrounds, eBaums World...

They also weren't a problem for small users either. Not only was there no incentive, they didn't necessarily get discovered by web crawlers. I remember wondering why my websites never showed up on search engines when I first started fucking around with webpages, web hosting, networks, etc. I hosted the server, I had a domain name, I was online and could access my site from other computers solely through the internet; but it never came up on Yahoo or Dogpile and I didn't know why. The first time I ever found my own site on a search engine, it was using a hosting site like Geocities. And that was after Google came out and I was getting archived versions of the first website I ever made.