I downloaded the Mass Effect 2 demo on my PS3 the other night. The PS3 version was rendered using the updated Unreal engine that Bioware is using to make Mass Effect 3.
Granted, the demo is a download and not full Blu-Ray quality but I definitely notice a difference graphically between the PS3 version and the Xbox 360 version. Some of the graphics are crisper. Faces are more realistic. The lighting in some places is noticeably better but, in others, seems worse (they chose to relight character faces in certain cut scenes. The changes aren't necessarily bad, but aren't optimal, either. Guess it's up to your personal tastes).
The responsiveness of the controls is a bit crisper/faster, which I imagine has to do both with the updated engine being used and the fact that the PS3 is more powerful than the 360.
Even though I've played through ME2 at least half a dozen times on my 360 (I have the most fun as an Infiltrator!), I'll probably get it for the PS3, too, so I can play it straight through on that system.
Only thing that sucks for PS3 owners who've never played the original Mass Effect is that ME1 won't be released on PS3 due to an exclusivity agreement with Microsoft. The "fix" for that on PS3 is that the major choices imported from ME1 are now contained in a digital comic book that the player reads through. Choices will be made within the comic that will effect ME2.
Of course, not nearly as great as playing the original Mass Effect (which had a better overall story than ME2, imo) but it's a creative way to fix that problem.