Lego_mindstorms
The new version of Mindstorms, Lego’s all-time best-selling product, was developed with the help of a Mindstorms User Panel, with the aim of developing a better product but also a tighter, more trusting bond between corporation and customer.

A lengthy article in Wired Magazine explains how it all worked.

Update 8 March 2006:
Another lengthy article just came out in CNET News.