The Shoton Festival is on June 30-July 06 in Tibetan calendar. In 2009, it is on Sep 20-26 in Gregorian calendar. Most tourist sites might be crowded with locals and some scenic spots may not be open to tourists. In this case, I personally suggest you advance or postpone your tour to avoid staying in Tibet during this period. If you don’t mind the crowds, it will be a nice time to experience the Tibetan culture.