I'm extremely curious about this and since my order hasn't shipped along with everyone else's, I was hoping someone that has gotten theirs already could do some harmless testing. My understanding of the i5/i7 lynnfield architecture in the new iMacs is that it has a re-vamped onboard memory controller that supports dual channel vs triple channel memory that the i7 900 series uses. Intel says that to offset the missing channel, lynnfield has official support for DDR3-1066 AND DDR3-1333 instead of just DDR3-800 and DDR3-1066 with the i7 900 series. Source: Anand's Lynnfield Review For whatever reason, Apple seems to have shipped these out with DDR3-1066 but I'm still curious as to whether or not we can squeeze just a wee bit of extra performance out of these things with DDR3-1333. According to Intel, it takes at least 3 cores pegged out to saturate the memory bandwidth but if you're video encoding, compiling, or rendering, I'm sure you could hit that mark fairly easily. So the question, could someone shove some DDR3 1333mhz in their imac and see if it's unofficially supported?