Had to jump in with this one. I was at WDW in September 2005 and went on both the Segway and the Behind the Scenes tours.
Loved, loved, loved the Segway!! My dad and I both participated and it was a blast! You get to see the World Showcase before they let everyone else in. It was also nice to zip around the lagoon in about 10 minutes as opposed to 20-30 minutes.
As a thank you for arranging the trip, my parents paid for me to take the Behind the Scenes tour. It does take about 7 hours. You start out in Epcot. They take you around the outside of the park, there's a road that basically circles the entire park. You also get to go inside the depths of the American Experience and find out how they operate that attraction. Then off to the enormous warehouse where they keep all of the holiday decorations (over 85,00 square feet, if I recall correctly...) You visit the manufacturing warehouse where they build the animatronics, and the cars for the rides. I actually got to sit in one the Expedition Everest cars! Awesome! Over to the Disney florists, with two divisions -one for the resorts and restaurants and one just for weddings. Then to MGM for lunch and a trip through the costume department. We actually were on the floor where all of the parade costumes are made. You end up in the Magic Kingdom just in time for the afternoon parade. You also get to go underneath the Magic Kingdom in the underground tunnel system. All in all, an absolutely fascinating look at what it takes to make WDW the happiest palce on earth! Every CM was excited to share with you what they did, I think it was because they could shine for a moment and they truly appreciated having the opportunity to talk to the guests. Highly recommended.