I find my self longing for Activate and Deactivate hooks for modules.  These hooks would run only when the module is activated or deactivated in the admin/modules form This would give module developers a convenient place to run on-time setup code (e.g. database setup) and a place to do cleanup once their module was deactivated. 

If there's interest I could create a patch for discussion.  Is there another easy way to accomplish these types of setup and cleanup tasks?