We went in 2005, September 25-October 1. Crowds were very light. It was extremely hot though, rained 1 day for an hour, but we loved it. We're going back this year at the same time.
In 2002, we went the middle of October. Actually it rained 2 days, the weather was cooler but the crowds were higher. Not much, but as some have been posting that must have changed in 3 years. Seems the crowds are higher now in October than they used to be.