I have; couldn't say enough good about the trip and Bill. I've been to two of his classes and on one guided trip so far, and going on another guided trip this year. You will learn a lot from him and have a great time to boot. Well worth the money IMO. He even made a camping/4WD convert out of Mrs. 1911 which I had nearly given up on ever doing. LMK if you have any specific questions.
I have NOT done an expedition with Bill, but did take his 2 day "on-the-road" class, and learned more in just a few hours than I had in years of trial-and-error method learning. He's a great guy, and I can only imagine the places you'd see, and the knowledge you'd gain on one of his trips. I am envious of anyone who gets to do these trips; we don't camp anymore, or we'd be there in a heartbeat if we did.
I did Hole-in-the-Rock with Bill in October 2008 and was extremely pleased with the trip. Bill is both a great guide/teacher but also fun just to hang with around the fire. He has kind of a dry sense of humor that I liked. Listen and watch and you will learn a lot, experienced or not.
Just be aware that if he says a trip may be technically challenging he is not exagerating one bit. HIR was a trip with some serious pucker factor. Be sure you call him and discuss a trip in advance before signing up.
The trips are pretty costly but worth every penny. He gets a lot of repeat customers.
Lee (1911) and I went on his Hotel Rock to the Needles Expedition from May3-7 and had a great time. I highly recommend a trip with him.
Ace mentioned that Bill's trips are pretty costly but I think this depends on how you look at it. What I mean is this, sure $925 is a pretty penny but you will be camping every night at no cost and eating only what you've packed. If you spent four nights in a hotel and ate every meal in a restaurant over those five days/four nights you'd probably spend several hundred dollars anyway. After having taken a trip, I think it is reasonable and am anxious to take another.
I have known Bill Burke for many years. You will not regret any trip you take with him. He's an outstanding instructor and guide, and just an all good guy. Here ar some pictures of a trip through Northern Colorado I did with Bill and a few guys from my old Jeep club. We started out at Jax in Fort Collins and went for 5 days ending up in Steamboat Springs.