With the "User Access Manager"-plugin you can manage the access to your posts, pages and files.
Exactly what I was searching!
A simple plugin that provides frontend usergroup administration for managing access to pages and posts.
Worked fine apart from the bug that has been found by others
http://wordpress.org/support/topic/plugin-user-access-manager-tweak-for-function-addusercolumn , for which fortunately there is a fix.
Great plugin. My only concern so far is the ability to restrict access based on custom taxonomie (custom post types). We can actually only restrict based on default taxonomie of "Categories"
Would it be an updated function for the near future ?