well I read lot of real Mac Lion Users over at the official Apple Forums that have the same error with non-dev builds ( aka AppStore/10.7/10.7.1 ) too.
Lion ( at least all versions that I have had on my Machine, Appstore as well as dev builds up to c37 ) contains bugs like hell and the kernel is obviously going crazy on some hardware combinations.
Yesterday Apple released a Graphics Firmware patch ( for ATI in iMacs ) to adress "hangs" on Lion. This wont help us here , but interestingly Lions graphics are abviously working different then Snows for the hardware. I am especially concerned because I wonder if my HD4650m would also be affected from this "firmware bug" ( cause the 4670m is found in some Lion-capable iMacs ) and what to do against that ( Snow 10.6.8 graphics/3D/CI/QE runs perfect on it however, and ZERO freezes)
I suspected it was related to the graphics card.
In 10.7.0 I had a lot of lag occurrence: everything would freeze for a couple of seconds then restore. This doesn't require you to reboot and do not make you lose all your work, but is obviously annoying.
When I updated to 10.7.1 I don't know how but this lag gone away. Now everything is perfect.
After trying the 11C40 (and modifying AGPM, AICPUPM, AppleHDA and geforce kexts to get back the missing hardware) I started experiencing this freezes.
So I'm starting to think it's related to something they modified in the video driver (?), but I have nothing to proove that.