hey guys - I fitted my SprintBooster tonight (thanks Franky!), and I can really vouch for this product (MY05 manual).
The car is really responsive - the surge of power is almost immediate. I'm guessing it'd shave 0.7 to 1 sec off the 0-100kph time (I counted in the high 5sec bracket as opposed to usual mid/high 6sec bracket), but someone with a G-Tech can probably confirm. It's abit colder here in Canberra at the moment though.
0-100kph isn't everything - It's great to only have to partially press the throttle and feel the surge of power in any of the first 4 gears (mind you, you notice the fuel economy figures soaring even on part throttle!). didn't really get to test 5th gear out.
For those of you worried about city driving, I honestly don't think it'd take too long to adjust to the additional responsiveness. In the wet when accelerating out of corners, I guess you have to take some caution. And take it easy in carparks too.
Fitment is easy. I did as Franky suggested and fitted it when the car was cold. Disconnected the battery, fit the SprintBooster, reconnect battery, turn until startup sequence then off again, then start the car up and let it run without touching the accelerator for 5 mins or so. Then drove the car hard. Not sure this sequence is really necessary thought The most time-consuming part is removing the plastic bit that covers above the pedals.
Yes, it's worth the money!

Black MY05 Liberty GT. Sti front lip, STi rear spoiler.
Hi-Tech Turbo-back exhaust (with quad tips). HKS Panel filter. Resonatorectomy. SprintBooster fitted.
35mm lower on Pedders Sports Ryder springs. Whiteline rear sway bar. 19" ROH Modenas.