My DH works in Middlefield, OH, which is apparently the 4th largest Amish community in the world (according to the sign, anyway) and there definitely seems to be varying degrees of restrictions placed on them. Our best friend's dad was raised Amish (in PA) but decided to leave before he took some kind of vow, in his particular group he was not shunned - our friend knew his Amish grandparents (has a quilt they made for him that is GORGEOUS). His dad said if he had taken his vows and then left he would have been shunned. Like amycrossley said, it varies between groups. Seems to be pretty permissive around here - especially before they take those vows - I remember going into a bar and seeing 4 Amish girls go into the restroom and 4 girls that looked more like prostitutes came out! But the groups I've seen discussed on TV seem much more strict - I wonder how much is just for TV?
When we first moved to OH we rented a house from an Amish family (they bought the farm, but wouldn't live in the house so they rented it out and built their house on another part of the property) and they were the BEST landlords EVER. Seriously, the day we told them about a problem they would take steps to fix it. My DH got a new 4-wheeler with a plow and loved playing with it so much he would plow their driveway too and since he wouldn't take money they paid him in baked goods - Oh. My. Gosh. SO GOOD. The only time in my life I was ever happy to see snow! Why did we move again??