I know several B riders that have a pit bike. They're definitely in the minority, but if you can afford it there's no doubt it's a hell of a lot faster than changing a wheel, especially if you're likely to be in contention.

I do not fit that description by any stretch. The series races I've been doing have neutral wheel support so I take advantage of that (2 separate pits! 9- and 10-speed rears! w00t!)