I just thought I would throw our experience in here, to give you a different perspective. We have been to WDW several times, and so when we booked our August, 2003 trip, we decided to do the KTTK tour, as something new and different. I researched the tour beforehand, so I knew what to expect.
Our tour guide was great! (I think his name was John). He was full of interesting facts and little known secrets about the MK, which I truly enjoyed hearing. I also LOVED seeing the parade floats up close. However, I have to say that in the end, I was a little let down by the whole experience. I think that seeing the "inner workings" of the MK sort of took away some of the magic for me. It really reminds you that the CM's are "at work" and that the MK is a place of business. I didn't think that seeing the characters backstage would bother me, but it did.
My fiance had a great time and thought I was crazy for being disappointed, but it's something to think about before booking. If you're a die-hard WDW fan, you might want to think twice before doing it.
Just my opinion...