I made good progress with facebook. I started with a daily budget of $50. Then I hit that 3 times in a row and they set me to a $250 budget. On the same day they increased to $2,000 again so I am pretty good to scale now. :)
I like the system because you can really get to a low cpc / cpm if your ad rocks (has a high CTR of 0,4% and up). I got an ad with 0,7% and pay $0,04-$0,06 now per click on that. But you have to use keyword targeting in order to accomplish that. Relevancy is key as always. That means you can get a good ROI if you have the right product that converts on Facebook.
But it gets my #2 ppc traffic source after Adwords now...
Of course their system still needs a lot of updates, first and foremost conversion tracking. Here is a little tool to improve Facebook Ads client-side: http://www.4houraffiliate.com/facebook-ads-manager (costs $200 USD)