I went to Yellowstone in 2009 with my Mercedes 190SL group. To the person who worried about wildlife on the road. In 2009 many bison were on the road but were not aggressisve towards cars. I had my Subaru with a moonroof and we were able to lean out and photograph the bison easily. They all came very close to the cars without any problems. Many bison around the cabins and near lodges. This is where you must be very careful. Tourists still being killed by bison when they get too close to the bison. Do NOT ignore warning signs.
Yellowstone must be one of the most beautiful spots on this earth. The hot springs with many colors are stupendous. I would recommend that anybody who can possibly go, go!