I had put up photos from the Fort Wilderness Segway tour recently, that is something new at WDW. I asked if Segways would be allowed around the campground for rent, and it looks like the answer is no. If there would be anyplace I'd feel was safer for Segways, that would be one place (more wide open spaces, etc.).
I am in good shape, but balancing on a Segway is exercise. It is also hard on the feet. And they go fast. I'd not want to put one in a crowded area, like on Disneyland paths. I didn't even always feel safe this past week when walking (through very dense crowds). I wouldn't feel comfortable with someone on a Segway in Disneyland. And I want to see Heelys gone too, while we are at it - too many kids running into other people.