Mannie Schumpert has done a nice job offering some practical examples using
map_meta_cap. Mannie also took all of the examples from Andrew Nacin's excellent WCSF talk from last year. If you are dealing with roles and permissions, the things from this talk are really important to understand.
As he notes, “instead of modifying your database to change the capabilities of certain roles (or specific users) you can modify them ‘on the fly', as Nacin says, by adding a filter in your