You'd probably rather hear from a professional that would have to deal with these things, but FWIW:

I think the device by itself is fine, the key is standardization. If I was hauled into the ER and the folks there could walk over to a terminal, plug in the device, and have my entire medical history immediately in front of them, that would be great.

Without that sort of organization, I can imagine the scene:

"I wonder if this guy's allergic to this med..."

"Oh, look. He's got one of those medical USB thingies. Maybe there's something on there that will tell us."

"Yeah, let's see. Dang, the admin's got USB ports locked down on this machine"

"I think Lisa in accounting has a machine we can use"

"Ok, let's go down there"

"Alright, we can access it... Woops, it's password protected. See if you can rouse the guy long enough to get the password out of him"

"Yep, that password worked. What the... Window Media Player wants to know what app to use when this device is accessed."

"Let's just close that... Ah, here are some folders. Now where would the useful stuff be...."

etc., etc., etc.

For now I'll stick with my more-or-less traditional dogtag (spiffy engraved one) with my name, address, home and work #'s for next-of-kin, and my doctors name and phone.