It sounds like general opinion is running against Segways in the parks. For the sake of presenting a dissenting voice, I'll say that I think people with mobility problems SHOULD be allowed to use them. We all know that sometimes wheelchairs are not used just for people with mobility problems. I have seen both regular and motorized wheelchairs used by parents specifically for the convenience of their children who were too old for stollers. I can't count the number of times I've been rammed by strollers and wheelchairs, and I've been bumped numerous times by people who really had no business trying to drive a motorized vehicle. In spite of all that, I still have no trouble with people using them if they genuinely need to.
Now, if someone genuinely has trouble with walking but could use a Segway, then I say go for it. If Disney is indeed forbidding them in the parks, I think it's pretty poor of them. Fortunately we've never had to worry with trying to load up a motorized vehicle for anyone in our party, and we've never had to to try to rent one at WDW. But if we did, it looks like the Segway is far easier to pack and load than anything else I've seen. Now as for whether or not someone would risk leaving it outside an attraction while they were inside, that's another story.