It should be fairly straight-forward to use ADODB or Pear-MDB2 abstraction layers instead of mysql_ specific calls so that the database type could be changed
It would be nice to be able to see what areas of the pages are being clicked. You could use the http://www.labsmedia.com/clickheat/
project which is open-source.
It would be nice to have a more exact location for the user based on IP address. Maybe you could incorporate the stuff from http://www.hostip.info
Since it is a big database that has to be maintained separately maybe this could be enabled in the admin section after you install the hostip stuff.