Road and Track did a test back in April 89 (I know, a LONG time ago!) and found that most of the products barely raised the octane at all.
Super 104+, which claims big numbers, only raised the octane by 2.2 points. So it turned 93 octane into 95.2 octane. They also found that if you doubled the dosage you didn't get double the kick, it only gave another 50% increase. So a double dose would only raise the octane by 3.3 points total (not 4.4)
A lot of these products will foul your plugs too (I found this with the use of 104+)
If you really need more octane, a lot of speed shops can locate race fuel for you. I know there is a race fuel place in my town which sells 98 octane, I used to run that stuff in my supercharged Mustang GT all the time.