A brief history of Fuel Additives

Okay, now I realize there are a lot of fuel additves (snake oil) out on the market that claim this and that without really doing anything. I've been sucked in numerous times without feeling any difference.
*I've only noticed a different on my motorcycle*
Okay, so I went to VP Racing Fuels (in Calgary) and talked with a guy at length and he gave me some stuff called C5. So I put in half a container into a tank full of gas and to my suprise I'm actually feeling a slight difference! The bottle claims 6-8 points increase in octane so that suposedly putting me at 98-100 octane. I doubt it, but there is no doubt the octane was increase *some* amount.
Has ANYONE else tried this product? I would recomend some others trying it for a couple tanks of gas and give their impressions on this stuff. I'm sold on the additive but I'd like to hear wide varity of feedback.
P.S. Has anyone used VP's Motorsports 103?