I have used some of Quest's (http://www.quest.com/sharepoint/
) software to handle much of the reporting that you are looking for at a farm level. Their administration tool does some pretty good reporting across your entire SharePoint implementation.
However, if Farm level access is permitted for a lot of your users, I would highly recommend that the permissions be revoked since this can be very dangerous. Farm level access allows users to make configuration changes to SharePoint that could make your SharePoint farm totally inoperable.