I'd say 1 mph, but if I had some dice to role, they might give me a different answer. Seriously, I think there's a few mph gain in average speed in my case. I live in Hilltown, so your mileage may vary. I'll see if I can get an answer from my GPS data, though.

The longest I've proven to myself that I can track stand is about 30 seconds. Most lights are longer than that, but major thoroughfares through residential districts that rich people don't live in, have long red lights. Whenever I come to a light and have to stop for it, I'll balance until the light turns, or I can't hold it anymore. The more practice I get, the better I seem to be at it. But I've been doing this for years; even before I went clipless, I used clips, and still preferred to keep my feet on the pedals.