I know you can create events in SharePoint for custom lists, sites, and etc: http://msdn.microsoft.com/en-us/library/ff728093.aspx. Unfortunately, they don't trigger within the permissions section of SharePoint.
I'm trying to find a way to capture the events in the permissions section. For example, I want to know when a user or group has been added to a site collection. Does anyone know how this can be done?