PS3 runs at 30fps average. Frame drops will go below 30 which is considered barely playable. 360 runs at 60 FPS which is considered good and very playable, and frame drops and whatnot will go down to 45. That also means, as they are both pushing the same graphics power currently, but the 360 is pushing double the frames.
“Adults are just obsolete children and the hell with them.” - Dr. Suess
Whats the point of even comparing consoles to PC's? You can't upgrade a console so they make a new one every few years that you must buy to play all the new games. With a PC you have the option of upgrading your current setup to handle the latest games.
It really depends if the manufacture goes all out on building both the ps3 version and the PC version. If you look at games that were originally on one console then later ported to another most of the time it doesn't look as good because it was not designed around the ported console or PC.
Now if the game is built for the PC then later ported to a console then most likely the PC version will pw3n the console version because it was originally designed for the PC.