If this is just a matter of RTFM, then I apologize for not having read every word of the manual, because I have not. But, seems to me that this warrants at least some word in the Xplained Pro manual. I read it very carefully and searched for both "F_CPU" and "MHz", turning up no hits.
So, can some kind soul enlighten me about F_CPU? AFAIK, I have not touched any fuses and have never invoked START onto this board.
Really, all I want to do is test some TWI code, but you have to set the bit rate to do that!