Just read an article in the Health Blog on Athena Health. Athena Health as you may know just had a very successful IPO. Although they initially focused on practice management functionality- medical billing etc, they have moved into the EMR space.
The back office "practice management" function (the medical billing) is a far easier nut to crack. Most doctors are already submitting claims electronically (directly or via a billing service). The EMR piece is more of a challenge and in some ways more "art" than science.
My feeling is that Athena Health should spend their efforts more on creating an interoperable "Practice management" platform in the same way Microsoft created Healthvault as a "PHR platform" rather then a PHR application. With Microsoft's approach, PHR vendors will use HealthVault as a backend platform to perform core PHR functions. In other words, Microsoft is not trying to take over the PHR space, but rather be a part of every PHR.
By creating a "Practice Management Platform", EMR vendors may design their systems to integrate with Athena Health's practice management functionality (this is done via a set of web services). The reason I say this is because those who know EMRs best are not the same people who know practice management functionality. If I was to design an EMR (which I am doing BTW), I'd much rather integrate well with a solid Practice management system than design my own.