We never used a tour guide but my wife and I did take a 'Keys to the Kingdom' tour a couple of years ago. We thought it was a wonderful experience. A cast member took about 10 people on a 6 hour tour of MK, both 'on stage' and behind the scenes. She showed us things that the public never sees like how they put the parades together and the costume and wig shops (both below ground). She told us annecdotes (like who are the people named on shop windows on Main Street) and treated us to a sit-down lunch in a private room at Liberty Tavern. We have been frequent visitors to WDW since its opening but this was our most memorable experience.