My experiences, in a coconut-shell...
Penguin Racing (or was it Riding) School, 1982. Taken for the sole purpose of getting a WERA competition license so I could get my thrills on the track instead of being stupid on the streets. A good introduction to track riding, with more emphasis on on-track ettiquite, flag communication and safety than actual riding techniques, though they did talk about racing lines, especially for turns 1 and 2 at Roebling Road raceway.
Motorcycle Safety Foundation riders course. Required at Ft. Bragg if you were a soldier with a motorcycle. The course as I recall concentrated on safely operating a motorcycle among the myriad hazards typically encountered by commuters on a daily basis. I learned a few things that may have saved my bacon.
Keith Code Superbike school, 1986. The traveling school was at Brainerd. The school concentrated on their method for improving your lap times. At that time, as I recall, the technique was to get all your braking done first, then do the turning. We did not do the drill where you go around the track without using your brakes, although I had read about this drill prior to taking the course. I had read "The Soft Science of Road Racing" years before, and had been using those methods (especially reference points) from the start of my affair with roadracing. I found the course useful, but I don't recall a lot of personal critique. I'd repeat if I were more serious about roadracing.
CRA riders school to get a competition license, I can't remember whether I took this before or after Keith Code's school. This was the one where the counter-steering stuff was demonstrated most clearly. No particular personal critique unless you were doing something that was so unusual it was likely to endanger yourself or others.
CMRA riding/racing school, 1989 and 1995? Again, just to get a competition license. The course was at Hallet, and covered pretty much the same stuff I had seen in previous courses, with a little more techhique than the Penguin school and a little more race procedure stuff that Keith Code.
American Supercamp, 2005. Now this was just totally different from road-racing. With it being a two-day course, there was more time to figure it out (or have it drummed into you). Lots of instructors, lots of personal attention and critique (Chris Carr stopped me during one session and said "you've got a roadracing background, right?" I nodded yes. "Well, you need to do the complete opposite of what you're used to..."). I took this course because I'm cheap and don't like being damaged. I get a kick out of trying to master sliding my XR100 into a turn in the flat-track style. If I can get my thrills at 15 or 25 mph on an XR100 at a friend's place for free, then I'll generally pick that over spending $100 or so for a track day at Hallet where I'd be going faster, but on an old bike (RD400) that is outpaced by just about everything else out there. I'll be doing this school again this year.