I put a 320GB drive in the PS3 but most of my games stream off the disc thankfully. Don't know how much space it's all taking up but probably not all that much. I'd be fucked if I'd stuck with the 40GB drive though. >_<
There's only 60GB or so left on the 360, but I have a lot of Arcade games on there and every single game I own has been installed due to the disc drive being a noisy bastard.