I fly on average once a month and I would say 99% of the time I do not have a problem. I have gone through the new back scatter machines multiple times and have only been patted down once and it was due to a moderately wet diaper. In fact, the TSA agent who patted me down actually asked if I was in an "adult protective garment" and if it could be wet. I had to say yes, and he said we'll be done rather quickly. He did a quick pat down and I was on my way. He was probably the most polite TSA agent to ever pat me down, so they are trained to recognize an adult diaper.
That being said, the behavior of TSA agents varies by airport. In some they are courteous and polite to the flying public. In other airports, the flying public are treated like the scum of the earth, with a lot of yelling out instructions and being just plain rude to the traveling public.
Best way to have a speedy trip through an airport, be prepared. Follow the TSA rules and be prepared. Just my opinion.