Before people act rudely to someone in a wheelchair, they should stop and think how they would feel if it were them. I don't know how many times someone pushing a wheelchair would be trying to cross a walkway or get out of a store and people just whiz by and cut the person off. We always stop and let them out and the people seem so grateful - now I know why. We do the same with strollers because we laugh and say that we can enjoy our freedom now, but in the future we'll be in the same boat, pushing kids through the crowds (when we have them).
A little bit of courtesy only takes a few seconds, but some people are in too much of a hurry. It's a shame that so many people's first instinct today is to be nasty and impatient, rather than to be nice.