This plugin shows which user has access to which posts under Users administration menu. User names are in columns so it is suitable only for smaller counts. Works only in conjunction with User Access Manager and requires PHP 5.3.
It was developed only as helper tool for another plugin which I am going to create in near future and I guess it can be helpful if you are interested how User Access Manager works. Plugin code is (or tries to be) well documented.
This plugin will probably not be updated any further. I provide no guarantees whatsoever.