I just did Brad's class today with some friends, and I highly recommend it. I used my personal ride, a wr250r, but my friends used Brad's bikes. All of us have a fair amount of street riding experience, and little experience on the dirt.
The exercises started fairly simple, but gradually added complexity. As the day progressed we didn't even notice as we blew past what we thought we could to on a bike. By the days end we were riding up, down, and across hills. Up and over logs, and in circles tighter than we thought possible. We were even riding up hills while navigating small rock ledges!
Everyone crashed at least once, but that is part of riding in the dirt. Once we got over our fear about that, things started clicking.
Brad ran an excellent class, and the pace was good for experienced street riders with little experience in the dirt. I went from being **** uncomfortable standing on the pegs to having it almost feel natural.