I've been an avid user of Google Health for a couple years now. Since the decision to end the service was announced, I've attempted numerous times to find some sense of replacement from HealthVault. HealthVault is a great service, but its hardly equivalent. For instance, HealthVault is merely a storage system for your raw data, and to view it or continue to keep track of it, you have to utilize other services (such as through the Mayo Clinic) with which HV interfaces to manage. It has a lot of possibility, in that you can utilize many specialized services from many different places, however it fails at keeping the experience seemless. You always know that you are leaving to a new site, and often times go through redundant logins and registrations.
Google Health however kept everything restricted to a couple pages. Your blood pressure measurements, weights and other vitals were displayed in concise graphs The greatest strength of Google Health was its stripped down visuals and your ability to create your own trackers for virtually any metric. I used it to keep track of my migraine headaches in hopes of finding a trend which would reveal possible triggers. Some of the services, such as the Mayo Clinic's personal health manager, which use HealthVault offer similar customization, but they are very stripped down, the interfaces are clunky and, once again, it takes an annoying amount of log-in's and desperate clicking to get into the service.
I wish Google would just release the source, so that someone else could construct their own version. I for one would. I loved it.