From what I've seen, the latter is manageable with bespoke anti spam measures backed by integration with systems like Stop Forum Spam or Akismet. If you then se

From what I've seen, the latter is manageable with bespoke anti spam measures backed by integration with systems like Stop Forum Spam or Akismet. If you then set new accounts to require manual approval if they do things that are clearly spammy (posting external links most notably, but sticking them in their profile right away is a good one to flag too), then you should be able to keep it under control. I've had no spam on my forum for the last six months or so doing this, and very few incidents over the last few years as a whole. Please note however that as with any social site online, this process gets harder and harder to control the bigger the site or service gets, since spammers want to have as much of an impact as possible with as few resources as possible. So while they won't try and modify their software to get round the anti spam measures on a forum with 50 members, they'll be more likely to try when it has 50,000 members, and almost certain to once it gets to a few million or more. Hence why Twitter, Reddit and others are in a constant battle to try and keep them out (your mileage may vary as to whether they're winning), whereas smaller sites can rest somewhat easier just by changing how the default registration process works.