S has been using the potty to pee on and off for over a year now. It was just a matter of getting him to use it all the time and to get him to poop on it also. And it was also a matter of training ourselves to regularly take him to the bathroom whether we're at home or we're out. I think that has been one of our biggest challenges.
In the past week, something clicked. S is happy to go to the potty whenever we remind him and often he will exclaim that he has to go, runs to the potty, rips off his pants and diaper/underwear and go. He has also overcome his fear of pooping on the potty. This has been a very pleasant surprise for us! For 5 days in a row he has pooped willingly.
I'm sure we're in for a lot of accidents and set backs but we're happy with this progress. But then again we're not surprised that this is how his potty training is going to go. S is just the type of kid that "gets it" when he's good and ready.