We did the Trek Travel long weekend trip to Vermont in October 2004. Basically, we did it to check out the quality of the company in a place we could drive to and bring our own bikes, before we booked a trip to Europe. The trip was the weekend after Columbus Day.
Trek Travel is awesome. Great food, experienced leaders who know how to work with people. Keep in mind that it will be cold in October and if you book during the first 2 weeks, lots of leaf peepers. Scenery is awesome. It was 30-45 in the mornings when we started. Unless you are riding around Lake Champlain, expect steep climbs. Our tour did the climb up Mt. Mansfield, which very few in the group actually did; I was not as experienced then and opted out, although I am sure I could have done it. Most of the people on our trip were triathletes and were astounded by the climbs! And, they made fun of us for having winter gear... well, I didn't see anything funny about riding in shorts and no-wool socks in a drizzle when it's 40-55 out.
The next weekend, it snowed in Stowe... so go early in the month! We did choose to go with Trek for our trip to the Czech Republic; they are pricey, but I think worth it. I like luxury after working hard. VBT (Vermont Bicycle Tours) is another good company; I know one of the leaders and she is very down to earth. They are a bit more moderately priced.