AdFreeZone - There is (or was) money in this. Slashdot at one point allowed you to pay $5 to remove ads (still might for all I know). I think Kuro5hin.org did something similar. I don't know how this is still relevant with AdBlock though.
Or did you mean something more than a community in a website? Somehow I can't help but be reminded of the "walled city" in Tad William's "otherland" books.
AfMijn - There are a couple of auction sites that implement short bidding periods. Google just found me bidz.com for example. I think finding a way to verify users as serious in an affordable way is what would get in the way of somebody implementing this.
ArticleBody - There is a service doing something similar, but I can't remember what it's called. Actually, it might be a firefox extension I'm thinking about.
DeadMansKnob - In the UK knob is a slang term for penis. Saying dead mans knob out loud will cause a lot of laughs.
exes4all - I know I've come across something like this before. It turned into people telling each others secrets and trying to hurt their former partners.
FossBounty - Sites like Rentacoder have escrow services. I don't remember seeing this applied to FOSS code bounties & it would be interesting to see it happen.
hardhacks - See instructables.com and plenty of other niche electronics hobbyist sites etc.
NoSEO - I wonder what Gabriel Weinberg might think about this.
WeWatch - YC funded a startup that was doing this a few years ago. I don't know what happened to them.
By the way, thanks for sharing :)