You won't see 3D support on 360 or PS3 anytime soon. For both of them there's not much documentation about the GPU and to make it worse the PS3 doesn't allow direct hardware access. It disables all 3D functionalitys and some of the SPUs work only half speed when not running games.
You can use your 360 as normal when you install Linux as it boots through a shader bug in the King Kong game.
Well, what else can you do with Linux? A LAN server, DVR or just use it to browse the web from your living room. Linux can do everything that Windows can but on a 360 or PS3 it's wasted power except when you won't to work deep on the hardware.
Everything that's "every day use" can be done by small x86 system like the VIA epia. They consume less power, are easier to modify and you can't add PCI cards to it.