I'm a long time lurker (ever since I test drove a Roadster) and I just saw this post so I finally decided to register. That's my website and a friend's project. My same friend recently built a small kart that uses a wii remote to steer, accelerate, and brake:
The WiiKart, a wireless go kart - Hack a Day
This weekend we started talking about our next fun battery powered project. I'll have to post it here once we actually make some progress