I've reworked the MPGuino (MPGduino?) a little by separating the display from the "logic" -- the display board can now be mounted separately from the Arduino-side stuff, which should make for smaller and neater installation. Also, I've added a small 2x2 jumper to allow for easier selection of backlight polarity. Finally, I've added a photocell and resistor that can be used to automagically dim the backlight at night, in bad weather, or whenever the interior of the vehicle is "dark" to help preserve night vision or keep the display from being a nuisance/distraction.
Schematics and board layouts on my blog: http://sites.google.com/site/adifferentlemming/Home/projects/arduino