This is directly from the ststurbo.com website describing the advantages of a rear mount turbo kit for passenger vehicles:
Benefits of Remote Mounting
Ease of installation. STS turbo systems can be installed in about 8 hours with standard tools and average mechanical ability.
Performance Sound. The turbo acts as a muffler and sounds like an aftermarket performance muffler. Turbo spool and rushing air from the blow-off valve make a unique sound that will turn heads!
No need for major modifications to your vehicle. STS systems are designed to "bolt-on" to factory mounts.
Increased gas mileage. Unlike a belt driven supercharger, the turbo utilizes "wasted" energy leaving your tailpipe. Most of our customers get 1-3 mpg increase in gas mileage.
Lower underhood temperatures. No need to worry about melting wires, hoses, or other components.
Converts back to stock in about an hour.
More room under the hood. Future repair work or modifications will not require the expense of removing the turbo system to allow access to engine components.
Cooler oil to the turbo. Cool oil is better for both the turbo and engine.
Approximately 500F lower turbo temperatures. Eliminates the need for a turbo-timer, which allows the engine to run after the car is shut off in order to cool down the turbo and prevent oil and bearing damage.
Denser exhaust gasses drive the turbo turbine wheel more efficiently.
Built-in intercooling. Intake piping provides ~50% intercooler efficiency. There is no need for the expense, pressure drop, and installation problems associated with a front mounted intercooler.
Turbo is exposed to ambient air rather than underhood air. Allows for better cooling of turbo components.
No need for expensive headers, mufflers, or exhaust systems.
Turbo is closer to the tail pipe outlet. Provides a better pressure differential across the turbine wheel which promotes better flow across turbine.
Better weight transfer. Increases traction because the bulk of system is mounted in rear of vehicle rather than up front.
Less noise in the passenger compartment.
Here is a link to their FAQ describing turbo lag:
http://www.ststurbo.com/f_a_q
Also, Two Guys Garage on Speed did a turbo conversion on an LS1 car, and it was making boost at 3g's just as described on STS' site. There is no turbo lag, IF you use a correctly designed turbo. The turbo these guys are using is WAY too big for such a small displacement engine as a bike. That's why they have so much boost lag, it is NOT the length of the pipe.
The only thing I disagree with on the sts site is that you don't have to use a turbo timer. I would not take a chance on it. If I had a turbo anything, it would have a timer on it. 30 seconds of gas is a lot cheaper than a $1,000 turbo replacement.