Is it possible to use a thunderbolt -> hdmi and usb -> hdmi adapter to drive two external monitors (non-thunderbolt) with the new macbook air? If not, has anyone had success with any other options?
I am planning to do this with my 2009 Macbook. Not thunderbolt, but a cheap USB or maybe the mini-displayport to 2 splitter--there are a number of options at monoprice in the $40-50 range (probably elsewhere also), might not be fast but it is cheap. There tend to be plenty of reviews for these products, so read them first (many people have done what you want to do).
Have a look here: Air powers three monitors.
It looks like it could be possible. I'm not sure about the HDMI adapting method though. I do not know of anyone doing that yet.