If... then... else
If access to this data was properly controlled, then great. It could be extremely useful for any number of non-evil groups.
If, however, it is handed out to any Tom, Dick or Harry, or simply leaked by mismanagement, then abuse is going to be a serious concern. As mentioned by someone earlier, insurance companies would love to get their greasy mitts on this kind of dirt.
...actually, now I think about it, poor data quality may make this database largely useless anyway. Data from clinical trials are often really difficult to interpret since doctors don't care/don't have time to worry about consistent data entry.