I have been looking for this video for some time now. This short excerpt from the MIX10 keynote shows how push notifications, which is meant to be a substitute for multi-tasking on Windows phone 7, works in practice, and I must say the implementation appears pretty slick.
What the video unfortunately does not show is what happens when notifications (the blue bar) stack up, but I am sure this will become clear soon.
See the video after the break.