I don't think it's lion to blame, I too have the 2010 air with lion and it runs just fine. Maybe spend some time with ps and find what process is eating your CPU. I'm not using file vault, maybe that's adding some overhead. I would recommend upgrading the hardware though, the resale on the 2010 air is pretty good, so moving to a 2012 isn't going to cost you much. I tried Linux on mine and it was a real pain.