We've been working on a couple of MPGuino installs. We began testing with a function generator to simulate the VSS (vehicle speed sensor) and the injector control lines. This allowed us to determine whether the firmware was working.
Once we got the basic firmware working, we were able to hook the circuit up to a Holden Commodore. The speed sensor is simple to calibrate if a GPS or similar alternate speedometer reading can be taken and compared with the MPGuino's readout. The injector calibration generally has to be performed over several hundred kilometers of driving to gain an accurate value for injector fuel flow. This will be performed once we're done manufacturing faceplates to neatly integrate the system into the vehicle dash.
The unit seems to be quite capable and will be a useful guide as to fuel consumption - especially useful on a large car. Quite fun to play with during downtime on the weekend!