I have to tell you that biking in Moab is great!! I have been out there dozens of times and would recommend it to any one who asks. I also recommend Kaibab bike tours. I did a 5 day trip with them to the grand cayon and let me tell you it was the BEST trip I have ever taken. The riding was amazing , the guides were great and the food,,, well let me tell you that I gained 4 pounds on the trip. The only thing the guides didnt do were ride the bike for you. I highly recommend it.
Riding in Moab can be a little tricky if you get lost you can die. It is a desert and water is not readily available, so plan accordingly. My suggestion to you is go during the fat tire festival. Its in October http://www.moabfattire.com/
it is the best time to ride there and they have guides for every level. Bring water bottles and some cool weather gear (in the mornings it is still cold). When I was out there last they had a Halloween ride where everyone dressed in costume and rode down main street to a pasta dinner (500 MTB) it was great.
Good luck Cori