Commissario
And @ Feek, i'd like to know this too, I want to move it to my boot disk, not my documents disk, I don't quite see why I'd want an app in my documents folder. :/
I've not done it yet but something has occurred to me - On the Mac Mini that the family use they all have Dropbox configured to backup their documents folder and this will add the Steam games to the backup and as it's the free version, it will overfill it. Bad.
At the moment on my Mac I have two folders within Documents, one called "Documents for Dropbox" which I backup and one called "Documents not for Dropbox" which I don't backup and as Steam dumps its files off the root of Documents I won't have a problem.
This is bad programming on Valves side, the Documents folder is considered sacred and third party applications shouldn't touch it.
Steam game files should be stored in /Library/Steam/*somewhere* and saved games/user details should be in ~/Library/*somewhere*, that would keep them clean and within the recommended OS X file formats.