Our practice has been using Vista / CPRS "WorldVista" for a couple years now. And we are now in the process of switching to something else because
- we cannot get Vista to meet federal meaningful use requirements.
- we cannot get adequate tech support to tailor the system to our practice.
And note that while is it public domain, you still need an entity to install it, train your office staff, run servers, etc.
It was far from free. Indeed, now purchasing our second "EHR" has made it an even more costly mistake.