Hi
I've not had any problems at airports with either the full body scanner. I was worried I would, but no one batted an eyelash!
Just prior to a pat down, I've said, "I have an ostomy bag on my right side, you will feel that." Some have made an effort to avoid it (maybe they were afraid of touching it). I always make sure it's emptied before clearing security.
I have traveled with a letter from my doctor but never had to produce it. Better safe than sorry.
I find with airport security people, the more upfront and honest you are, the better it goes. I've never been asked to step aside or go to a private room. If I was, I would be nervous, but keep in mind, they are doing their job. They don't know me, and I don't know them. I may not be Angelina Jolie, but in that case, when it comes to getting checked out at the airport, I am one in a million! :)