[zorkerman]

I think a big problem in this space is liability, as a medical provider you have legal protections that help defray some of the liability associated with breaches in data, and more importantly subpoena power from the feds. Any data a user gives to you has to be given freely by the patient, bypassing HIPAA, and thus making that data available to parties it would not otherwise be available to.

This is the real reason only the big guys like google and MS are really trying this out IMHO, because they've got a big checkbox to face the potential legal ramifications of this problem.