I just wanted to throw this out to people having all the trouble with their new 21.5 and 27 iMacs. Go get a early 2009 refurb instead. Prices are incredibly cheap and you know they will work perfectly.
http://store.apple.com/us/browse/home/specialdeals/mac/imac
http://store.apple.com/us/browse/home/specialdeals/mac/imac