Writing a spam filter is kinda fucking hard.

WOT is cool, but it's a band-aid that excludes newer users. 
POW is also cool, but most Spammers can get around that super fucking easy, so I don't really see that as a proper solution. 
Micropayments are also not a solution in my mind. 

What I'm doing so far kind of seems to be working, but I also block my own posts from time to time.