I fitted my Power Box (http://www.power-system.co.uk) on Thursday last week, and after some initial teething problems, it's running fine.
So... I thought I'd better tell you all about it!
Basically it's a natty chrome box (about the size of a pack of playing cards, maybe a bit longer) with 5 wires coming out of it.
These 5 wires are spliced into existing wires going into your ECU.
It works by fooling your ECU by altering signals coming from various sensors in the engine. The ECU responds by increasing fuel and timing (I think!)
The result... More Torque!!! The car pulls away nicely even in 5th (obviously not from a standing start
!) I was messing about on the way home tonight accelerating away in 5th and making myself grin 
...Really easy to fit, only took about 1 hour to solder it all in and make it look nice, we had a few problems, but I'm going to contact the manufacturers asking that they improve the instructions. If the instructions were 100% it really would only take an hour tops (if your mechanic/auto electrician is good at soldering!)
The manufacturer states that different ECU's need differing amounts of time/mileage for the box to be fully recognised.
Anyway, I've done just over 200 miles since it was fitted and I'm starting to feel a lot more torque.
They recon that if you're not leathering it, the fuel consumption should stay about the same. If you've got a lead foot, expect about 10% less mileage out of a tank (compaired to ragging it when standard).
Anyway, that's me done for now... I'll let you know if my fuel consumption goes crazy or if anything goes wrong as soon as I know!
Just for info, I'm going to get to a Rolling Road soon to see what difference it has made.
) 
