Here is an interesting video of our local Madison racing. I'm always looking forward, so I never see the rearward view like this. These races typically are about 10 miles / 16km in length (80 laps of 200m) at average speeds of around 33mph. I never look at my speedometer at the sprints (or ever really in a non practice race), but the top speed has to be close to 40mph in the sprints.
The rider is wearing pink, so any time you see a pink jersey, it is at the point of a hand-off. For instance at the 2:50 mark, pink comes in hot at over 30 mph, hands off to his team mate (with the camera), and quickly falls back as all of his momentum is transferred to his team mate (its quite a rush when done well).
The handoff and sprint starting at 4:10 is strong enough to throw the team in front of the green team (that is how you do it when it goes well).
Don't worry, its not the whole 10 miles on the video.