John, thanks much, this is useful!
What I'm working on – I'm a mentor for an FRC robotics team, developing intro to robotics classes/workshops for our team members and kids in general. We want to use the GoPiGo as our teaching platform. For programming, it looks super. For assembly, a good start if it doesn't prove too delicate (12-year-olds, tiny screws...). For mechanics, however, we need to add devices (which I'm pretty sure will require a larger platform with more widely-spaced wheels – no problem and a good lesson - and auxiliary power). The soccer-ball herding prongs are a good start, and I'm looking into a spring-loaded ping-pong ball shooter. We can start with a kicker, an arm, a climbing hook... that aren't on a moving robot, but eventually we need to put the pieces together.
We're particularly interested in using the GPG because we're working on modifying our FRC robots to use a RasPi instead of the standard RoboRio controller, and it would be sweet to train our students on this platform from the beginning. (One of our mentors developed the nav-X XMP navigation sensor [http://www.kauailabs.com/category/products/], and he's the one who suggested we check out the GoPiGo in the first place.)
I can post here to let you know how we progress.