It's a mix of things; Deck, AdSense (for all the trouble they're still a major and these days fairly steady source of revenue), mostly-passive Amazon affiliate, and direct support from the MetaFilter community.
We've looked at other ad rubrics and been disappointed with the specific performance we've seen in a couple test cases, but the volatility of the ad economy means that it's certainly something we'll be reexamining continuously as time goes by.
We've looked at other ad rubrics and been disappointed with the specific performance we've seen in a couple test cases, but the volatility of the ad economy means that it's certainly something we'll be reexamining continuously as time goes by.