I second that feature request; besides other useful ways it can be used for, it would help in large groups with many mods.  For example, we have about 10 part-time mods in one of the groups I admin and having a visual indication on the main member listing screens would be helpful when trying to coordinate member approval as it would help eliminate sometimes-duplicate efforts.

I can also see where keeping specific-notes like Samuel does is also helpful, or as in keeping records for troublesome members for example.

Cheers,
Christos