FB.api: Error 500, callback function not executed.

Question

FB returns error 500 and says: (got this from the net tab in FireBug)

FB.ApiServer._callbacks.f159e9f3f5816a({  
    "error": {  
       "type": "Exception",
       "message": "(#341) Feed action request limit reached"  
}});  

3 questions:

1. Have any one else encountered this ?
2. How do I get the response/callback from the server if it returns 500 ?
   I've tried to use FB.api callback (cb) parameter, but in the cases of 500 it never comes back. (unlike 200OK).
3. How can I know what is the current limit, if possible ?

For example:

Let the user know after it failed: "You can not post any more. come back tomorrow". Or even: "You have 5 posts left."

Does any one knows if the limits are per app OR per app per user ?

Thanks for the help.