Yes it does have an API, and some sample apps. The .NET samples include a web application to talk to the service - however, I give up on it for the time being as the utility to make certificates seems to crash all the time (nice unhandled error, by the way; the crash seems related to the fact that the app is installed in Program Files as opposed to Documents, and Visual Studio doesn't have full rights to PF). Will come back to it later, but so far it is remarkably similar to Google Health.
One additional thing, the SDK features some device drivers to enable medical devices to talk directly to HV. Nice - as long as they don't cause any crashes...
