Thought about this one too, but have not found much info on what you get to do.
It's subject to change, but when I did in October of 2013 we met the tour group outside the gates of EPCOT. From there we...
1. Got a brief tour of the backstage areas of EPCOT and the World Showcase from the bus.
2. Watched a little of the American Adventure from the behind the stage work area where you can see the machinery that moves the stages/sets/figures in and out of position.
3. Briefly walked around the American section of the World Showcase before it was open to the public, being shown things about forced perspective, etc.
4. Drove through the back streets of MGM and toured the wardrobe design/production studio workshop they've got back there.
5. Chatted with one of the mechanics at Tower of Terror and got to look in and underneath one of the ride vehicles sitting in their maintenance bay.
6. Lunch at Whispering Canyon
7. Toured Disney's topiary garden/greenhouse facility.
8. Saw some of the backroads of Animal Kingdom and walked through the hangars where the Jammin Jungle Parade floats were being kept/charged up.
9. Toured Central Shops. This was the highlight. Got a close look at a ton of stuff being worked on, including the 7 Dwarves figures, most of the Jungle Cruise, Astro Orbiters, etc.
10. Entered the Magic Kingdom via the utilidoors behind Tony's. Walked around there for a bit, popped up on the other side of Main Street, then watched the 3-o-clock parade go by.
11. Went back to EPCOT and were dismissed.
Interspersed through all of this is guidance/lecture by a pair of tour guides, both of which were dudes in their 40s who used to be instructors at the Disney Institute. A lot of the time you're out of the bus you have radio headsets you can use to listen to the guides while in a park/facility.
Your actual itenerary will probably vary depending on timing and whether certain areas are safe to enter.