I know a few people who have run Prochargers with great success. One guy I know of was making close to 1,000 horses on a small block Chevy V8 and knocking down around 18mpg at the same time. As everyone has said above, the packaging may be a little tricky, but it would be easier than a roots type or a turbo setup I would imagine.
In my opinion however, turbos are better. They don't require a belt-drive which means they don't involve the parasitic loss associated with superchargers. They also convert otherwise wasted exhaust energy into power. Finally, they are an "on-demand" type of system... they won't go into positive boost unless you are putting your foot into it, which means you should be able to maintain good fuel economy while having the power you want (i.e., you can have your cake and eat it too!).
Downsides of the turbos though are packaging, lag and heat. Routing all that exhaust pipe can be tricky. As far as lag goes... with a properly set up system it isn't an issue... but if you are just running one big turbo (as opposed to multiple smaller ones, or a single smaller one) it can be a problem... when you're in a turn and suddenly the turbo spools you're back end will come wide quickly. Also, since turbos spin at a mugh higher shaft speed generally, they put out a lot more heat than a supercharger. This might not work too well with the fiberglass rear bonnet.
I love turbos though... = )
John
