I should also add that most over-the-counter boosters claim gains "up to 7 points" in octane. The truth of the matter is that with the RM/2 method (which is the method you see at your local gas pumps), a "point" is actually 0.1 and not 1.0. So adding 7 points to 91 octane is like saying you are now burning 91.7. And for a car that was experiencing detonation/pinging with 91, the extra 7/10's might just be enough to suppress the condition. Thus, people think it's great stuff!
To each his own, I guess.
I think I'm going to also look into local race gas suppliers (for grins). So long as they are not adding alcohols, you then know with more certainty what you are getting, and for how much.