It certainly is a nice ride. I rode the Königsee-Bodensee route in summer 2005. Although it was raining for a significant portion of the trip, that didn't seem to make it any less enjoyable to me.
BikeLine have a indepth guide for this specific tour, they have excellent guides to most long distance routes, however they are in German only.
I can highly recommend that tour, there are some good hills too.