I ran a forum for a while where we would ban people to a "penalty box" where that would be the only forum that they could post to or see until they worked their way back out. It was pretty funny (un-registered users couldn't see any forums unlike pinside).
It was a good alternative to banning someone from the forum because everyone could still interact with them and some users enjoyed being in the box and then didn't want to be left out. users could still PM folks and use all of the other features.
my biggest beef is only around the long threads where everyone feels like they have to comment, but not add anything to the discussion. The only solution I can see to this is to have a post sort/order ranking like Reddit where people who just blab on about nothing are downvoted? I don't know if that will work as it will just end up being a popularity contest and then everyone sad about downvotes.
-c