[quote name='utopianmachine']Say that I get this for the Xbox. Can we download games directly to it and play from there? Also, if I format it for the 360, can I still use it for other computer-related things and have it still work in the 360?[/QUOTE]
You can use it like any other 360 memory unit or HDD, so yes you can download demos, install games and store profiles.
As far as using it dual 360 and PC, yes you can, but you have allocate how much of the drive will be used for both I believe.