I have a Windows 7 (32-bit) box with 2 users, both admins (my wife and I are both developers). My admin account was created during Windows setup, hers was created later. Both accounts are in the same groups, yet we have VERY different permissions. In the beta and RC, both accounts worked identically (RC to RTM was a fresh install on this box, not an upgrade).
I have a C:\bin folder with the sysinternals utilities and a bunch of other stuff. Running anything in there or in system32 just works on my account, on hers I get access denied errors (cannot access file or path). If I right click and try Run As Administrator, I still get the same thing!!!