The GumBrix article: http://armyofevilrobots.com/node/378

The gumbrix came about because so many of my robot projects required the kind of rapid prototyping that Lego® really excels at, yet required more in the way of control electronics than Lego® was capable of. With a maximum of 3 motors and 3 sensors, the Mindstorms kit was not really capable of the more complicated control strategies that I was interested in. For example, it is possible to build a balancer, but not one with a touch sensor and proximeter as well, and certainly not one with arms. At the same time, custom machining every single part for a balancer is VERY time consuming, and not flexible once assembled.

In retrospect, the solution should have been more obvious. I have built a controller for lego parts that is capable of offering far more processor power, unlimited sensors, and a large number of motors/pneumatics.
The GumBrix Specs:
* Gumstix Waysmall 400MHz Arm7, with bluetooth, 2x serial, I2C, and Linux
* Delrin case with Lego compatible studs and rails
* Custom interface boards with AtMega8 running as an I2C slave
* Modular Jack for interfacing