Bitcoin and Altcoin Discussion especially, and it's probably because a lot of sig spammers know they can post garbage there without having their posts deleted by mods--and it's true, because there are so many shitposts in those sections.

The gambling sections seem to attract people who are genuinely interested in gambling topics, but there's still a lot of spam last I checked.  There are a lot of members who can't write proper English but who persist in trying anyway, and the result is a mess.  Not sure about Trading Discussion.  I think there's a lot less spam there (in a relative sense), but it's still pretty bad as far as I know.

This has all been discussed ad nauseum, and it's pretty common knowledge how bad the situation is.  Theymos doesn't want to censor members, and I think that's why the problem has persisted.  But hey, at least we got the merit system and the requirement for 1 merit to rank up to Jr. Member.  That put a huge damper on account farming and the ability to earn money by shitposting.  Those actions didn't solve the problem, but they helped.