My 2011 MBA has been having problems running my thunderbolt display, and having applecare, I took it in to an apple store near Portland, OR. I told the representative that it lags severely when the thunderbolt display is hooked up. He grabs a display from out back, hooks it up, and we start a video from hulu. The video lags to about 2-5 fps, and is unwatchable. Moving windows around the display shows severe lag. He plays the video on my air, and it runs fine. At this point, he proceeds to tell me that there is nothing wrong with my computer, and it simply is not powerful enough to run a 27" display. I told him this is ridiculous, and it shouldn't have any problems doing simple tasks, and that I'm not expecting to do video rendering, but find it inexcusable it can't handle the monitor. I know others have had this problem, but that it is a problem with some models, and is not a problem with the MBA design itself. A IT guy from Cupertino, who now is a graphic designer who works with my friend, said this was irregular behavior, and I should have the computer swapped out. The rep told me that playing video is a high intensive process, and that the thunderbolt display has "a lot of pixels, and I shouldn't be able to expect my MBA to be able to handle such an intensive process," and proceeds to go to the specs of my computer and tell me that it isn't able to run a thunderbolt display. He told me they could take my computer for 2 days, and spec out a similar MBA to see if the other one was capable of video playback, and running the thunderbolt display more capably. I couldn't believe what he told me. It's one thing if my problems are unconfirmed, or another to say they'll take it and see what's wrong, but to straight up tell me that it's not designed to be able to run the display left me dumbfounded. I was in a rush by the end of it, so I said I'd come back in a few days, but as I left, I thought "does this guy realize the new ipad screen has more pixels than the thunderbolt display? Is he gonna try and tell me the ipad is more powerful than my MBA?" I'm now calling apple support to see what they can do for me.