Depends on where your PS3 is placed as well as how much room you have around it. For example, heat rises, so if you have your PC say in a higher part of a TV cabinet it will be a few degrees warmer up there than at the bottom, as well, make sure you have a few inches around your PS3, I cant remember what the book says? 2-3 inches probably? myself I have my PS3 literally about 2 inches off the floor (and it is concrete floor so it's very cool) and have all sides exposed. I have never had any issues. My 360 on the other hand... but that was my stupidity, had it sitting on top of my subwoofer, which I discovered gives off a bit of heat.
Surprised I never had any scratched discs in my 360, with the subwoofer pounding, woulda thought a game woulda scratched by now :P
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