http://www.us.playstation.com/PS3/about.html
The above link mentions that the ps3 may not be able to play certain ps1, ps2, and DVD movies. This is something that hovered over the ps2, mainly both models and while I wouldn't be mad at Sony because a few games don't work, it's something to think about. I was thinking that by now, we could avoid an issue like this. Maybe not.