Keep private notes about each of your users that only Administrators can see.
This plugin adds a text editor area to each User Profile in the dashboard for Administrators to keep private notes about each User. The notes are ONLY visible to Administrators -- that's the whole point! It also adds a column to the "All Users" list where you can quickly see the note for the user without having to even open their profile.
It is especially handy for Membership Sites where you may have thousands of members to deal with and need to remember special circumstances for them.