Let me be clear: I'm not suggesting that Evernote is a substitute for any of the excellent commercial EHRs currently available. The following is presented as a proof of concept only for how a simple, inexpensive, customizable EHR built on Evernote might work.
Evernote has confirmed by email that, "At this time we do not plan to pursue HIPAA certification for our (consumer) Evernote service."
Of course, if you're concerned about transmitting information to the Evernote servers, you can always instruct Evernote to keep all data on your local computer. This bypasses the HIPAA issue and you'd still be able to use Evernote, but this means that you won't be able to access patient data from the web unless you use a program like GoToMyPc.com.
How Doctors Can Use Evernote As A Professional Memory Accessible Anywhere, Part 2: Using Evernote as an Electronic Health Record (EHR). EfficientMD, 08/2008.