Breaking down at Disney World is far worse for those waiting their turns than it is for the ones on the ride.
Disney does a pretty good job of getting guests back on a ride after it breaks down. Either by giving those guests a fast pass for a return or simply letting them hop back into the front but for those waiting in line, it isn't fun.
Spaceship Earth - Imagine a long day in the heat and jumping on Spaceship Earth at EPCOT, then getting all the way up to the top where the Earth can be seen as your car enters "space" only to come to a jolting stop. 30 minutes is a great nap and let's be real, no other ride offers a better chance to get one in. Now, if you are stuck listening to Lady Judy Dench talk about the Phoenicians, yeah you might go nuts.
The great EPCOT ball breaks down all the time but many of those stoppages are due to wheelchair-bound guests getting on or off the attraction. At other times, they are simple stops that may last a few minutes. I would find it quite interesting to have to be escorted out of the ride. See the lights come on and walk the pathway back toward the exit. That might be kind of cool.