I just went to gary semics school at his home track in Ohio. It was, in a wrod AWESOME. It cost me about 200 a day wiht bike rental, more for the flight out there. I believe is is 100 a day.
They teach many techniques and I really learned alot. I can start and go through the whoops almot as fast as gary and I have video to prove it. My corner speed is at least twice as fast though.
A couple of catches;
1)You must be willing to learn.
2)You must have enough ability to be able to do the techniques they teach while you are concentrating on riding. For example, alot of people in the class did not even attempt to do gary's techniques after repitition of them. They did not have the skill to do them.
3)You MUST listen intensely, ask questions, be alert, and DON'T interrupt.
The most important of the above is #2. The parents of the kids that did not try to do the techniques really just threw their money away on the course. What a waste. The kids did not seem to leave with anything more than when they entered.
If you are ready, go for it.
If you have the money, I would recomend going to Gary's home track. He has some specially made sections to help with special techniques and the track was watered and groomed ALL day. No rocks, perfect dirt.