IMHO people who need the handicapped stall wait in line with everyone else. Once they get toward the front of the line the people ahead of them may choose to let them go as soon as the stall is next free, but otherwise they get to the front of the line and then let others ahead of them (for the regular stalls) until a stall opens up they can use. Yes, it's *nice* for people to let them cut ahead, but it's not rude not to unless the handicap also means they can't wait.
I end up using the handicap stalls all the time now - they're often the location for the infant changing tables, and also the only stall I can fit both me and Babybartfast when she needs to go. I would assume someone with a visible handicap is capable of waiting the same way anyone else would unless they told me otherwise.
I completely disagree that a handicapped person should wait in line for the ONE stall for them while everyone else has several stalls. If it comes open and they are waiting in line, then they should move to the front when the handicapped opens. No one knows their disability. I could never stand there and take the handicap stall knowing someone disabled was waiting for the one stall they can use.
I don't think that handicapped people actually have to wait significantly longer than anyone else to get a stall, due to how the system works.
Here's how I see it:
Let's say there are six stalls, 5 regular, 1 handicapped. There is a line, so all stalls are constantly in use. Assuming people going steadily in and out without any extreme delays, which could happen in a regular or handicapped stall. If a handicapped stall opens up, and a handicapped woman is within the first six people in the line, I think it would be very kind to let her go in, as a regular should be open shortly. However even if the first person in line does not do this and instead uses the handicapped stall, the handicapped woman will be the very next one able to use it, as the remaining people ahead of her would have already entered the newly opened regular stalls.
That means that at most, the handicapped woman is delayed by one person. If the woman is far back enough in line (say number 20), it doesn't make as much sense to let her jump the line due to unfairness, as she wouldn't have gotten into a stall based on her current line position, even if all six of the stalls were handicapped stalls.
Of course, I'll let anyone who is about to have an accident go ahead of me, handicapped or not. But they have to say something, I'm not a mind reader.