I'm in the process of making my USB install for my new upgrade from Mountain Lion to Snow Leopard.
I've had it with ML after a couple days. In all fairness, it is better than Lion, but even with 8 gb RAM and 512 SSD on a core 2 duo (MBP 2010), I can see a degradation in speed from SL.
Memory management appears to be more efficient (this is a subjective) than Lion, but I find that there is a serious bug with the MBP sleeping and recognition of RAM (sometimes it would recognize only 4 gb as opposed to 8 gb). I would have to restart for it to properly recognize the amount of RAM. I have tested with remtest and everything came back fine. I even took everything apart and shopvac'ed all the dust out and cleaned out the actual memory banks. I also tried other RAM modules and saw the same problem: everytime it goes to sleep and doesn't wake up, a hard reset needs to be done, and then only half the ram is recognized. You have to shut down the computer disconnect the magsafe and then turn back on and boom: 8gb of ram.
But stepping back and looking at the overall quality of Lion and ML from SL, it reminded me of the infamous xp to Vista by microsoft.
Anyways, my USB install is made. gotta go.