I'm on a late 2011 MacBook Pro and have had no issues with 10.8.2.
It looks as if you have a hardware problem. You could try running the Apple Hardware Test to see if you come up with any hardware errors. If you do (or even if you don't) I would take the machine into your local Apple Store or an AASP and have them run their diagnostics on the machine - because I don't really think that it's an OS problem.
Thanks for the advice! I'll try running the diagnostics.
On the other hand I'm using 8Gb of Kingston memory (certified to work with my Mac) so I'm sure if I bring the Mac to the Apple Store with those modules they'll tell me immediately that it is the problem
Therefore I guess I have to go back to my older 4Gb modules that came with the Mac and hope until it freezes again (it's going to be a pain running with 4Gb again... hello virtual memory paging!)
Although this never happened with Lion... even with my 8Gb Kingston expansion it has always been rock solid
I doubt if it's the RAM - and the folks at the Apple Store don't give two hoots about you installing your own RAM. They even have instructions on how to install RAM and HDs for goodness sake!
So... just run the AHT and see if you get any errors. I would bet that it's something other than your RAM.