I've got one of those Diablo Predators as well as a copy of HPTuners.
The Predator can only be used on one car at a time. Once you download the performance tune from it into a car, then it is basically "locked" to that car for the duration. However, when you restore the factory tune, then it is unlocked and you could use it on a similar model car compatible with that unit. The Predators are pretty specific about which cars they will work with.
You CAN use it to scan multiple compatible vehicles, but just not use it for the performance tuning on more than one.
HPTuners is sold with an odd sort of licensing arrangement whereby you buy credits that can be applied in various ways. You can use these credits either on a "per vehicle" manner, or via a "per model year" arrangement. In other words, you can use the base credits to tune three different vehicles, all different makes and model years, or you could arrange it so that you could tune ALL C5 Corvettes. I believe the program also has the facility such that if you do the "per vehicle" method and sometime down the road tune several of the same makes and models, that this can be converted to do the "per model year" arrangement instead so you don't wind up paying more "per vehicle" of a type that you would be better off simply paying for the "per model year" method.
For instance, suppose the "per car" license runs you 2 credits and the "per model year" license is 6 credits (this is just for demonstration purposes, I don't remember the actual credits for each). And when you buy HPTuners you only thought you would be tuning one 2002 Z06. That costs you 2 credits of the total you got for free when you purchased the program. But then a month later a friend asks you to tune his 2002 C5, which you do, costing you 2 more credits. Then another one comes along with another 2002 C5, for another 2 credits. At this point, you have already used up as many credits as it would have taken to use the "per model year" license, so you can convert the licensing at that point from the "per vehicle" method to the "per model year" method. Which means, that now ALL further 2002 C5/Z06s can be tuned for free without requiring more license credits.
EFILive is supposed to be another highly rated PC based tuning program, but I have not looked into it myself.
There are several other handheld tuners available, but they all are pretty much going to marry you to an individual car's VIN number when you use it.
Although these are all interesting tools to play with, and some will be better than others, depending on your particular circumstances, in reality, NOTHING beats having an experience tuner work on your car for you with some method of direct feedback on the results of his/her tuning. A combination of a dyno, and just seat-of-the-pants responsiveness are what you are looking for. A dyno will normally only give you PEAK readings, which is nice to know, but you also want to know throttle responsiveness and just all round driveability of the car after the tuning. So try to get a combo of dyno/street tuning to get the most out of the potential of your performance.
In my humble opinion, of course.....
Tuners/ Programmers
and leech off your thread, as i'd like to know as well!
bro...
It's not like I am going to discover some hidden power there that got overlooked. 
Linear Mode
