just got back from the tetons/jackson hole/yellowstone. the tetons and surrounding communities are incredibly bike-friendly. i wish i could have been there a month. i used to do a canada fishing trip every year. after this trip, i'm thinking of replacing it with a scenic cycling trip every year.
the big downside for me was that the area is very expensive, "touristy" and commericialized. yellowstone and teton n.p. are basically zoos without walls. i felt sorry for the animals as the paparazzi followed them with camcorders and cameras.
one of the best rides i had out there was when i went out into rural wilson, wy. incredible.
also, despite being one big slum....i found council bluffs, ia to be a cycling-friendly town...i wouldn't take a vacation to ride there....but not bad for an overnight stop.
yellowstone otoh....i'd stick to the bike-specific paths. the main roads are too narrow/scary.