One of the many challenges of being a MySQL database administrator is the inability to account for high server usage. While some current tools provide good reports on overall activity -- none report usage by individual users, a specific database, or connecting client to help DBA's identify usage hogs among web hosting clients.
Software Workshop developed their own modifications to Open Source MySQL and called it ExtSQL and it's something you might want to look into. It gives DBAs a simple way to monitor activity by individual users, database, or even connection.
MySQL has an installed base of millions, with many installations running older versions. DBAs can be very reluctant to go through an upgrade process. Software Workshop decided to pursue this huge 'aftermarket' by offering source patches and binaries for older versions of MySQL on a variety of OS and hardware combinations. ExtSQL is being released under the GPL.