mnet is Moodle networking, it is a way of letting users roam between Moodle sites, if the administrators of both sites want to allow it. It is quite new and a bit notorious for being poorly documented and having a few bugs, but both those issues are being worked on, and it can be made to work - I went to a talk about one example at the NZ moodle moot last week.
Notes is an addition to the user profile to allow people to make notes about other users.