Same here. I can't find the way to reproduce this. Here are messages that I get in the console when freeze occurs:
02.08.2012. 2:55:58.000 PM kernel[0]: **** Debug info for *possible* hang in MAIN graphics engine ****
02.08.2012. 2:55:58.000 PM kernel[0]: ring head = 0xd720ec58, wrap count = 1721
02.08.2012. 2:55:58.000 PM kernel[0]: ring tail = 0x0000f288
02.08.2012. 2:55:58.000 PM kernel[0]: ring control = 0x0000f401 enabled, auto report disabled, not waiting, semaphore is waiting, length = 0x010 4KB pages
02.08.2012. 2:55:58.000 PM kernel[0]: timestamps = 0x2ac9298
02.08.2012. 2:55:58.000 PM kernel[0]: Semaphore register values:
02.08.2012. 2:55:58.000 PM kernel[0]: VRSYNC: (0x12044) = 0x2ac9298
02.08.2012. 2:55:58.000 PM kernel[0]: BRSYNC: (0x22040) = 0x0
02.08.2012. 2:55:58.000 PM kernel[0]: RVSYNC: (0x 2040) = 0x0
02.08.2012. 2:55:58.000 PM kernel[0]: BVSYNC: (0x22044) = 0x0
02.08.2012. 2:55:58.000 PM kernel[0]: RBSYNC: (0x 2044) = 0x0
02.08.2012. 2:55:58.000 PM kernel[0]: VBSYNC: (0x12040) = 0x0
02.08.2012. 2:55:58.000 PM kernel[0]: trying to clear semaphore wait on MAIN ring
02.08.2012. 2:55:58.000 PM kernel[0]: After attempt to clear semaphore wait = 0x0000f401 still waiting
02.08.2012. 2:56:03.000 PM kernel[0]: stampWait: Overflowed checking for stamp 0x2ac92a1 on MAIN ring: called from waiting for blt buffer (3D blt)
02.08.2012. 2:56:03.000 PM kernel[0]: timestamp = 0x2ac9299
...and this keeps repeating until I turn off MacBook Pro (13" Late 2011, Intel HD Graphics 3000).