The Gears series and Mass Effect are my only regrets for not having a 360. All of the other stuff that interests me is either already on the PS3 or is coming (i.e. Bioshock). I don't care if I get it later on the PS3 than the 360, as long as I get it. I would definitely jump on Gears for PS3.
Keep this in mind when reading what I type...
I've been gaming longer than many of you have been alive.