Forgive the LOLCat speak, but I felt it appropriate.
The new Steam update came out today, and from the Settings dialog you can opt into the Steam Community beta. (My page is located here.)
If you're running Vista, the Steam Service gets installed as part of the update. As far as I can tell, the service exists solely for the purposes of bypassing UAC so that Valve can write into the Program Files folder at will.
Gee, wouldn't it have been easier just to code to the Windows development guidelines in the first place? My only real problem with Steam is that it replaces one set of guidelines for another, completely incompatible set of guidelines.