While doing some testing for a topic on GMF, I came across a glitch that seems to be very important.  A moderator can't demote an owner, nor promote someone to owner.  However, in this test case, a moderator with all permissions was able to remove an owner's membership from the group.  In at least 2 locations, the membership overview and the individual member record, the Remove function allows an owner to be removed.  I didn't try it with the last owner, but I don't think a mod should be allowed to remove an owner at all.

Thanks,
Duane