Just to be an arse, on my board (though I'm admin) I use the function as a 'get the mod to do something with this thread' function.
This includes 'please rename this thread to...' and 'can you add the poll...' or 'please merge with...' and so on.
I feel the report post function is an under used feature, as people always kick up a fuss in feedback forums if there's anything against the rules etc.
Note: This is ONLY to be used to report posts which break the rules (like spam, advertising messages, and problematic posts) or are posted into the wrong forum.
Just kill the word 'only' and let people use it how they like.