>>23
SA solution: Pay money to post, trolls/crappy posters either donate huge amounts of money to register many times or are turned off by the cost. Additionally this pays for the servers!
Problem: People don't like paying money for Internets.

2ch solution: Screw all attempts at stopping trolls and crappy posters; just ignore them.
Problem: This practically invites spammers to your forum.

99.9999% of forums solution: Registration prevents crappy posting lol
Problem: Hahaha. This isn't a solution at all, c.f. most of the top 10 forums I listed!

Both models require huge amounts of volunteer moderation, but on a popular and enjoyable forum it's easy to find good volunteers. Considering that Western forums evolved from old egotistical BBSes, I think SA is the pinnacle of the registration model. But 2ch is a far better solution, I agree. Too bad we don't know Japanese ┐(´ー｀)┌