I rode one for the first time today. It was at the police department and a police model, complete with flashing red/blue LED lights.

I can only imagine how a pursuit on a Segway would go.

They have already been used to sneak up fast on bad guys.
They are really cool. The new ones are so much more streamlined than the 1st generation. I got the hang of it within about, oh, 30 seconds. If you have good balance you'd be fine. I was told that plenty of people can't seem to get the hang of it. The police chief ate it hard going over a speed bump resulting in much blood loss and stitches to the face. Ouch! To give him a break though, riding on wet pavement and hitting bumps can be challenging.
I can't agree that they will change the world, as they were hyped, but still a great invention.