i've had drivers wave me through intersections lots of times, and if there's no one else waiting, i usually go (mostly it's when i'm stalling and trying to avoid unclipping/stopping). i always make sure to give a thank-you wave. i've also had a few cars cheer me on, and while i'm not always sure if it's serious or messing with me, it's harmless either way.
on the flip side, i almost got hit today. car in front of me slowed down, so i went to pass on the right. as i did so, they started turning right onto a side street. i squeaked by just in time for my back wheel to escape their front fender. they should have signaled (they didn't), but i guess i should also have been more wary of why they might be slowing down.