Why genetic privacy could be doomed

I was having a discussion with some friends who have all expressed interest in being genotyped or have been about putting their information into the public domain. They were a pretty savvy lot (half of the six had been genotyped), but one expressed the common sense objection that "someone could find something in the future." In other words, a really creepy stalker could keep running your data through Promethease. Imagine you're a really strange person, and you have a bunch of gentoypes of people who you want to know about, and you design a program which scours the academic literature and constantly notifies you when the individuals in your database pop up with a large effect mutation. I have no idea why someone would do this. Perhaps you could be blackmailed by someone threatening to disclose to your employer than you had a 50% greater chance of a heart attack ...