My pony, Bandit, is very nearly broken to drive... we're just going to refine turning and get him a bit more used to pulling with a person in the cart. He'll mostly be used for fun, since there aren't any harness shows near me, and I might rent him out at the nearest town's "Graf Days" for little kid's cart rides or something. I'm trying to talk my saddle club into including driving classes, though.
Dante is learning to drive, too, but he's only been hitched to the cart maybe once, so... he's further behind. ;p
I hope to eventually drive them as a pair, but that's still awhile off, I think.