Using both on a 57 inch 1080p Flat screen, I can say at least for myself, no. I never really notice that much of a difference. There are definitely differences between games meant to be released exclusively then ported, but a multi-platform release never really seems to have enough of a difference, at least for me. There usually is a small graphical upgrade, but not enough to warrant buying the PS3 over the 360.
But again, that is my personal opinion. You may have your own which differs from mine. Good for you, I respect that you have your own opinion so long as you respect that I have mine. If you don't respect that I have mine, I don't give a shit what you think anyway. I'm simply adding my opinion to the matter based on the knowledge that I have observed first-hand.