The general public bias against Segways is kind of understandable. Most people aren't capable of thinking outside the box. I'm always a little surprised when the hacker/entrepreneur community seems to jump on that bandwagon though. Even moreso today when so many people claim to be "green" advocates and will proclaim that we need to explore other modes of transportation, yet bash anything that doesn't have 4 tires and a steering wheel.
Sure, the Segway has advantages too - but when people suggest that it should go at 25mph in city streets, it's worth considering whether the Segway's unique properties actually contribute anything. Different tools are better for different jobs.
I'm all in favor of thinking outside the box, but things like cargo bicycles are more practical and interesting (though less sexy and high-tech) for my own city transportation needs: http://www.xtracycle.com/cargo-utility-bicycles.html
A closer comparison is a scooter or moped type of device. Those will fit through some doorways, but being gas-powered they are generally excluded from use or storage in most indoor areas. Cost is comparable, although the scooter would win out on distance and top speed. Most scooters are also too heavy for a single operator to pick up and move, and they also don't generally break down to fit easily in the trunk of a vehicle.
Segway's, even the non off-road models do quite well on dirt/trails, so that isn't an advantage for the bike. They could go in the streets as well, the only limitation there is erratic legislation, so it's hard to make a direct comparison.
This would be worth the extra money and not be uncool.
I had to laugh at the thought of a Segway doing 70mph. I'm all for taking risks, but have you ever done 50mph+ on just a moped?
As for this bit - "imagine something that worked like the Segway, but that you rode with one foot in front of the other, like a skateboard. That wouldn't seem nearly as uncool." - have you seen the Scarpar? It's only 35mph, but definitely, definitely cool.
This similar idea, though:
http://www.youtube.com/watch?v=Gm_2PnSkWck
... maybe. Looks a bit wobblier, but look at it in context - they are on a cycle path and they fit in perfectly well. Someone on a Segway would stand out quite a lot.
(The "dork factor" is what prevents me from doing the smart thing and wearing a skate helmet. Instead I only wear a pair of wraparound shades. Stupid peer pressure...)
I've never ridden a segway, but I have crashed my bike at this speed. I imagined that it would be really bad, but having done it a few times, it is really not that bad. You are moving parallel to the ground, so most of the energy is absorbed by the pavement slowly grinding the top layer of your skin off. Somewhat painful, and very bloody, but not life threatening.
I imagine that riding into a wall at 20mph would be pretty bad, though. All that energy instantly acting to crush your bones and internal organs. I haven't actually tried it, so this is just speculation. (Please report back if you try it ;)
(Oh, and as for the helment; I always wear one, but I have never landed on it while crashing. Let your arms and legs do the work :) I think you have to do something weird to land on your head.)
EDIT: Although I was very dazed at the time, my ankle was actually injured worse than my head.
Hey, I even have a picture: http://rants.jrock.us/post/55729583/good-idea-riding-your-bi...
Not weird, just reckless. Like tolerating faulty rear breaks for a little while. What was I thinking :)... Anyway, the helmet took it and the dog that prompted the full stop got away unscratched...
Also, did you use your front brake? I tend to see my rear brakes as a backup; I use it if the front brake fails, if the front wheel has poor traction, or if I'm descending and just want to slow the acceleration. The front brake can develop about 5x more stopping force, since the front wheel can't skid. And, if you are used to using it, you won't go over the handlebars in an emergency. http://sheldonbrown.com/brakturn.html
I used both but only the front worked. So I landed on my helmet, bike on top. Quite the other way than you, I tend to use mostly the rear break. Not being used to rely on the front, not in a "to the floor" way anyway is what got me. That and the lack of proper adjustment tolerated to the rear one.
Also, nice link. Thanks.