I think Segways are great for sightseeing tours, and I've done (and enjoyed) a couple on my travels. Segways basically created a new way to sightsee.

I can't imagine how tours would be able to operate 12-15 mile 2 hour "walking" tours otherwise. You're able to see a significant part of a city from eye level without a huge amount of physical effort.

There's tours like those in quite a number of big cities, including San Francisco. Whenever I was in the city, I'd see them all the time.

I've seen that in the States as well. Pretty much the only time I've ever seen Segways "in the wild".