I like them, I'd get one if they weren't so expensive!! Oh, an available already...
I'm pretty sure it's still in prototype stage.
Several similar systems have been out for a while now, and none (as far as I'm aware) are in production yet.
Stuff I would find useful:
1) Speed. When you're in traffic, having your speed, RPMs etc in a HUD would mean you don't take your eyes off the road
2) Satnav. Same reasons as speed
3) Track days. It stands to reason that you could probably upload a track map, to give you the best lines with optimal braking and acceleration zones, like in GT4.
4) I'm a sucker for technology?