Lil' brown man hit it right on the head. IT'S ADDICTING! My car WOKE up and felt quite quicker then it did on pump (could be that race gas was in the better window for the turbo vs. psi).
As stated, your cat will die. Your o2 will die. You will also foul more plugs, but that's not too terribly bad. Lead in the gas is what kills it. But, if you are like a lot of other people, you don't have the cat, o2 to worry about, and you keep a box of plugs in your center counsole
When tuning/driving on race gas, try to keep it as one or the other. I wouldn't mix the gasses that much. Going from race gas tune to pump gas tune I don't really care-if anything it will run a bit rich. But, when I swap to race gas, from pump, the car is pretty much dry as can be. I'd even have a 5 gallon tank in the trunk, so when I run the car out of gas, I then have the race gas to put in it.
-A. Swift