I've been having strange issues with my iMac too.
27" iMac, Mid 2011 edition, 3.4 i7, 16GB RAM, AMD Radeon HD 6970M with 1024MB ram. 10.7.2
I have a Macbook Pro as well, and used migration assistant to transfer over my files. All seemed good for about a week. Then upon waking from sleep or rebooting, I'd get strange graphical glitches and programs continiously crashing. The glitches ranged from garbled pixels on menu bars, garbled pixels on the desktop and even one time where the desktop would blink between a grey screen and the image I had selected.
Verifying the disk showed that there was a problem with the drive bitmap, and I had to reformat and install all over again.
Again, for about a week things were fine and then the problems started up again. A call to Applecare and I reinstalled Lion without deleting my info.
Rinse and repeat, it seemed fine for a week until I got strange graphical glitches again and none of my programs besides the apple ones (safari, itunes, ical) would open, just crashing repeatedly. I re-downloaded Chrome and was able to run it from the DMG and after a reinstall on the hard drive, but a restart made both of these options crash.
I've done hardware tests and everything turns out fine, verified the disk and it's a'ok. Tested the ram with rember and that's fine too. Even ran S.M.A.R.T. and the drive checks out. I made a new user account but the problems with crashing applications persisted.
Now I'm on a fresh install of Lion and just waiting for something to happen. I'm still unsure if it's some sort of software glitch or if it's the hardware. Any ideas?