Like many others, I will use a handicap stall if I know I'll be quick, there's no alternative (and that could include a filthy stall or clogged toilet, which I had happen just the other day), and nobody else there wants to use it.
But just for the sake of discussion, I'll share this. It opened my eyes a little bit.
For the past two years, I've taken my elderly mother to Disney. The first year, she was mobile and could walk into stalls on her own, despite having a walker, and take care of business independently.
This past year, her mobiliy had greatly decreased, and she had recently gotten out of rehab after a full hip replacement for a fractured hip after an accident at home. She was in a wheelchair and needed help getting out of it, onto the toilet and back, and assistance with clothing and sometimes cleaning, etc. In other words, a big job, which required one person being there with her and another helping with equipment and supplies, for safety as Mom could not stand alone on her own too steadily. So my DD and I had to tag team to accomplish this with each and every bathroom use.
It is not always easy finding bathrooms to accomodate something like this. The best one is over by Soarin. But I digress...
At one place I remember, the handicap stall was down, so we had to take her into a regular stall but leave the door open in order to roll the wheelchair in there and help her transfer, etc. We could barely move. DD tried to block the doorway as much as she could, but Mom was embarrassed and humiliated that things were this way and we had to help her like this, etc. We didn't mind, but it was awkward.
The one, though, that sticks out in my mind the most was the time when Mom really had to "go" but there was a Mom in the only handicap stall with several girls and they were in there for over ten minutes, probably more like 15. (A couple of pp's here alluded to this, too.) They were laughing and having a good time, in no hurry, and I suppose could've had hidden disabilities but none were evident. They all just walked out afterward, with not even a stroller. Waiting was excruciating. Other people in the bathroom were getting upset on our behalf, even, and made some comments like, "Hurry up, there's someone waiting to use that stall" watching us wait.
I guess the moral of the story is that if we (myself included) do use a handicap stall, to do so quickly in case someone who has little other choice of which stall to use, has to use it as well.