I already have this on my "todo" list ... it will show-up on the popup menu on post titles (and also on the action menu for a post).
Who reported it and the reason will be listed (only the mods will see) but instead of sending a PM, there will be a separate 'X alerts' displayed for mods and a shared list showing the reason etc... Not decided yet if I should let people put comments (possibly useful) or just select the reason from the drop-down list (as per edits)