Others have pointed out the issues and difficulty of anonymizing the data, but I'd also be concerned about Google having that kind of data because of their existing business relationships. Google's current customer base is large and small corporate advertisers the world over. If they have a new set of data available internally, I find it difficult to believe that they would not try to sell some kind of service based on that data to their existing customer base. Without extremely strong corporate governance the temptation would be just too high for someone to say "I know - let's make some of our anonymized health records available to this existing large customer of ours."
