Think William Weld, the governor of Massachusetts who had his data re-identified by MIT students after challenging them that it couldn't be done (not smart, that)
There are at least a couple researchers at the National Library of Medicine who publish on this topic.
It is not a yes/no thing, there is only the balance between privacy and potentially groundbreaking research.
Of course the data can be re-identified. Just by using a few of the PHI protected data item... zip, age, sex, dx... one could possibly determine to which of your neighbors the data belongs.