kwtolman,
I am the 2nd owner of a 1991 Callaway Twin Turbo Corvette. In 2005, after several years of ownership, I took it in for restoration and in the process did quite a few upgrades.
Callaway has always been regarded as the best in terms of power, styling, professional engineering design and craftsmanship, and standing behind their products. My experience with them reinforced all I had heard and read. And this was with a product that is not current technology -- at the time 14 years old.
At the moment, I have a 2008 C6 on order and plan a Callaway conversion when it drop ships to them.
Supercharging is now commonplace. The Supercharger on my 2000 Jag XKR has been very reliable and knowing that Callaway has not only done the research AND testing, are the exclusive distributor for Magnusen for Corvette, and warrant the work they do, I have the higest degree on confidence in the product that they sell.
As for warranty coverage I am sure that you will discuss with Peter how Warranty will work with them and/or your dealer, but I would expect to find a dealer being a Callaway authorized sales/service facility at least in major cities. I know that there are some dealers already selling the Callaway Supercharged 560 packages.
I have been told that gas mileage with the 560 package "on the Highway" remains about the same but of course it only makes sense that "spirited driving" will require additional fuel

- the same applies with my Twin Turbo Corvette now.
Callaway has produced a few Callaway Supercharged cars already (look for pictures on this forum), and I have confidence on their work and products.
It will take a long time to remove the smile from your face once you feel the power and look of the work on your car.
I hope you also consider joining us at the Callaway Reunion at Corvettes @ Carlisle this year (Aug 23-26) in PA, you will meet quite a few owners and some of the Callaway Staff.
Regards,
-Luigi
:cool