In case you didn’t know, the PS3 can run Linux. Not only that but it’s officially supported by Sony. You can download (for free) a utility to put a boot loader on to some media (most likely a hard-drive but memory cards, memory sticks and anything else the PS3 can read (and can hold 10Mb) are supported) and set it to boot “Other OS” (that’s what the menu says).
There are already videos on the Internet of it running Fedora. Zac Bowling already has one running Mono, a task simplified by the fact that the cell processor appears as a PPC.
So where does the Xbox 360 come into this? Well Microsoft are releasing something called XNA, a modified/extended version of the the .NET 2.0 run-time with emphasis on Managed DirectX that is available for Windows and the Xbox 360. A version of XNA called Mono.Xna that is built on top of the Tao framework is in development. The end result is that in theory, games developed using XNA will run on Windows, Linux, Macs, PS3’s and Xbox 360’s.
A few problems still exist. The processor that the PS3 uses is rather strictly an in-order processor so most stuff that isn’t written specifically for that will run slowly (although video playback will be pretty zippy) and so far there is no hardware 3D support for an “Other OS” so XNA (if it were available now) would run slowly.