I'm an individual contributor to Google Health Co-op and work on the non-profit Palo Alto Medical Foundation's tagging efforts @ Google Health Co-op as well.  I'd be happy to speak regarding how tagging is improving health search on Google.

http://www.enochchoi.com/thoughts/archives/002164.html

http://www.google.com/coop/profile?user=000834671960008790965

http://www.google.com/coop/profile?user=001677525886229228418

I posted my answers to "4 Questions" call for answers...