He's been standing unassisted, even playing with both hands while standing, for several months now, but he has simply refused to walk.
Our theory is this: although he obviously has the balance, he's become such a proficient "pusher" that he doesn't want to slow down to walk.
Miles started pushing a cute little wagon when he was about 8 months, and has become increasingly steady and now super fast with the wagon.
Then he learned to push the little shopping cart (with swivel wheels - an extra level of challenge but also extra maneuverability).
Now, although he can walk, he knows that running behind a small table or a tipped stool is much faster, so he does that in stead!! Who has time these days to toddle around anyway??