I understand that cities in the area of the Grimm Brothers have developed a sightseeing road that goes for many miles....has anyone done this trip ? Any comments ?

I spent a weekend in 2011 exploring part of the German Fairy Tale Route...it was wonderful! I planned my trip using resources I found at http://www.deutsche-maerchenstrasse.com/en/. The site used to have a very good interactive map, although I could not find it tonight. Try the "Brochures" tab, the site says you can order information. We spent a night in Alsfeld (super cute town), then visited the Junker Hansen Tower, visited Schwalmstadt and Hannoversch-Munden, where we spent a second night. From there, we visited Dornröschenschloss (Sleeping Beauty's castle) and the nature park/zoo near its base...wonderful. Our final night was in Trendelburg Castle (Rapunzel’s castle). The trip on the Fairy Tale Route was one of my favorites in the 3.5 years I lived in Germany. Have fun!

The full tour from Hanau to Bremen is about 350 to 400 miles, depending on the number of detours you take. Of course, you can shorten it. The middle section through Hessen is most scenic with lots of historical small towns and villages and castles. However, Bremen would be a good finish because it has a fine old town and a spectacular historic city hall.

Germany has invented so many sight seeing roads it is part of their marketing. I particualarly like their "Carrot and Swede" road in the Pflaz

Yes, it is marketing. It is not a special road but more a suggested itinerary using ordinary roads. But the fairytale road is worth it because it lead through so many picturesque towns which are off the beaten path.