I have a 3.4ghz i7 27" iMac with the 2GB graphics card. Both on DP4 and the final app store version of Lion have had this weird graphics glitch where every once in a while, all of the shadows behind windows turn into half transparent grey blocks that extend 3/4" around each window, and my dashboard widgets are all garbled. A restart is all it takes to fix it. I've tried permissions repair, and have done all updates, but the problem persists. Any ideas?