The early review of the game that got pulled said the PS3 had much more of a population on the streets. The 360 version has a more cartoony look and more bloom lighting.
Here's a link to a copy of it before it was yanked by Take2
http://home.comcast.net/~infamousdd/CGReviews_-_Cam_Garish_Reviews_-_One_Review_at_a_Time.html
Both games will be great, but early indications say the PS3 being the lead dev platform paid dividends.
360 version has "pop-up" pedestrians and cops. The PS3 does require an install, but the install seems to keep the pop up people and draw distances down.