Paging Dr. Google
What people who use Google need to be careful of is third-party applications they might sign up for. There is no law prohibiting them from selling your data.
Quick: When's the last time you had a tetanus shot? Who was the doctor taking care of you when you had it? And how many overstuffed folders would you have to rummage through to figure that out?
For nearly two years, Google has been offering free accounts at google.com/health that allow users to store, organize and, should they choose to do so, share their health data with a doctor, family member or caregiver. Google Health won't say how many people have signed up (and neither will Microsoft HealthVault, which has a similar product). But it's starting to pick up on the business side.