c248316c_rom_a_SharePoint_Administrator__Notes
[Action] User Security Reports [Alternatives] SP Admin toolkit and PowerShell scripts are free utilities but these are not as easy to use. SPFarmReport, is a CodePlex alternative that allows you to generate holistic reports for all uses [Notes] 
This feature allows the administrator to display which sites and lists/libraries a user has access to within a site collection. It also allows an administrator to view which AD groups an account is part of.
Steve´s SharePoint Space | Another SharePoint blog, from a SharePoint Administrator
Notes