I recently upgraded from 10.6 -> 10.7. First thing I noticed, incredibly laggy system; I figured maybe it was since I hadn't done a clean format in about 3 years, so I went ahead and did an "old-school" format. Clean install from a 10.7 DVD I made. The problem? Incredible lag. Whereas previously i could multitask with no problem, now if I have a YouTube video running in one frame of Firefox the other frames become dog slow loading and the video drops to <15 fps. Forget about flash video full-screen, which was previously no issue on this computer. Opening "folders" in Mission Control is laggy and choppy - overall everything seems to have slowed to a crawl. Multitasking is almost impossible without getting the beach ball to some extent between opening programs. I am running a late 2008 2.4 GHz Macbook Pro with the RAM maxed (4 GB), so the system is far from old or underpowered (my opinion). It's bad enough that I am contemplating going back to Snow Leopard this weekend and doing another format. Any suggestions? Edit: I should mention that the problem does not appear to be isolated to Firefox: Safari has the same issue with full-screen Flash video. Choppy and unwatchable.