Josh Barro's mother is on Medicare and her doctor has stopped taking Medicare patients because of the ACA. Barro views this development as mostly positive:
The explanation [the doctor] gave to his patients is that PPACA’s new requirement for no-copayment annual wellness visits is too large a burden for his practice. "Wellness visits" include some, but not all, of the components of an annual physical. He could start doing 15-minute wellness visits, but he’d rather continue giving long, expensive physicals, and he has patients who are willing to pay for them or who have private insurers willing to do so.
This is a great example of why the Medicare cuts are not a free lunch but are still good policy. There are a wide variety of perfectly suitable doctors in my mother's area who take Medicare and whom she could go to instead. Making sure all the most in-demand doctors take Medicare is a lower policy priority than making sure everybody gets some level of health insurance.