Mountain Lion sharing and permissions: two things I didn't know

Didn't know, or forgot:

• If you option click the permissions add icon, you can add permissions for System and the like but not Wheel.
• The Groups defined in Contacts can be used to add permissions to sets of users. I think that's probably as old as OS X, but I forget it. It's odd because Apple seems otherwise to have forgotten Contact Groups exists. I wonder how it works ...