My PCP has joined with several other practices and a Hospital to form an ACO. While you are correct that Medicare isn't talking about this; my practitioner/office was. I will quote from letter I received: ...on July 1, 2012 Medicare plans to start sharing certain health information with us about your care......" My immediate reaction was how would they have my detailed health information that only my Doctor has now. I opted out (declined) to have my infomation "shared". According to the nurse in the office, many of her patients also objected to this information sharing. Don't know how this will turn out.