There are several issues with this that have been brought up - and there are several more people should know.
1. it has been done by several other companies and there is a reason it hasnt taken off
2. for security purposes only critical lifesaving info you are comfortable having exposed, lost and stolen can be made available
3. these usb devises can easily be overlooked, lost or even destroyed in an accident
4. this key information is often needed asap when a computer is not available - such as in the ambulance or at the scene
5. for security reasons many hospitals block access to the usb ports on their computers so this may very well be completely irrevelant as they may not be able to access it in the ER!

I suggest anyone interested in having their emergency medical information available to responders take a look at www.wellalarm.com
it is not perfect but it a substantially better solution.

..with my security hat on, the option of creating an "encrypted area" on the USB Drive means that complacency sets in and then the wrong data can get stored in the wrong area.

I've seen it with "optional" areas on USB Drives..it only takes one bout of "oops, I forgot to log in and store it on the protected area" to create a problem. The less the user has to think about, the more you reduce the risk; the more, the higher.

The answer is fully encrypted stick but that defeats the purpose of being used in case of emergency....

So, the answer is - don't store anything on the USB Drive that you wouldn't want made public so, if it is compromised, you haven't exposed yourself to too much damage. Blood type, allergies, etc...fine (with a few caveats). Passport details and identifiers - think again.

Just my two penneth...

When I was responsible for the responding to emails from a major Insurance company. I came across the same concept being touted by another company...in 2006!
Shame I never saved the email or the name of the company who was offering 128mb (it was 2006) USB drives for the storage of medical info.