I received a 4GB kit of OCZ PC2-6400 DDR2 in the mail today, immediately installed it, doesn't boot in new iMac... So i figured, great it's DOA... I put everything back in the box and was gonna call Zip Zoom Fly in the morning to get it RMA'd, but after googling on it, the iMac doesn't like to run 800Mhz ram at 667?? A person also said that G.Skill PC2-6400 doesn't boot. Of all my years building PC's I've never heard of a computer ever in my life not to be backward compatible, go go Apple.