I have the 60GB launch 'fatty'. It sits on it's own unit next to the TV and has a good 10 inches on either side and 15 inches from the back to the wall. The built in fan does increase in volume when my gaming sessions last a while, but I have frequently been at it all day, usually a Sunday, when playing games like Oblivion. I'm talking from 10am-5pm straight.
I don't believe in cooling fans, because I read somewhere they can actually blow warm air back into your PS3. Not what you want.
As for the endurance races in GT5, I won't be bothering with them unless you can save your race every now and again.
24hrs on a console? Madness!