While I have not had the honor of attending, I've heard wonderful things about it. The programming is done by the National Science Teachers Association (definitely a great organization) and Math Solutions (which I'm not familiar with, but it was founded by Marilyn Burns, who has some phenomenal ideas for teaching math, so I'm guessing it's a stand-out organization as well).
It's an all-expense paid (including travel) week at the Liberty Science Center in Jersey City, NJ (an excellent facility), with lots of opportunities for learning and socializing with other like-minded teachers.
I believe there are generally a very large number of applicants for the 100 available spots, but there's not much to lose by trying (the application is short and pretty simple) and there's potentially a whole lot to gain!
P.S. Application deadline is October 31!