Segways are great for mall cops. I think for commuting they suffer from being neither fish nor fowl. They are not really fast enough for riding in the street and they look as though they would be difficult to provision with lights. I've never seen one ridden in the street (but then, I scarcely never see them other than in malls, airports and such with cops on them).
On the other hand they are too fast for sidewalks. Fundamentally, sidewalks are for pedestrians.
Overall I guess they just seem less practical than alternatives like bicycles, scooters and cars.
On the contrary. I think they're perfect for suburban sidewalks. Suburban sidewalks are empty most of the time and a "rush hour" would involve two people passing each other in opposite directions.
Distances are long. If you need to travel 2-5 miles it's really too far to simply walk (unless you have a lot of spare time) but if you can maintain 8mph on a segway for most of the trip a 5 mile trip is about the same time commitment as a 2 mile walk.
They might not belong on urban sidewalks. And unfortunately they're expensive and unfamiliar enough that suburban American will be afraid of them an unwilling to give up their Tahoe (for a normal car) in order to buy one.