Wired Magazine has an article about "decoding your DNA". The company 23AndMe will, for a grand, "take a sample of your DNA, scan it, and tell you about your genetic future, as well as your ancestral past".
There's obviously a long-term concern about a Gattaca-like scenario (gene discrimination). But in the short term, is it possible that health insurance companies will make gene testing mandatory to apply for coverage? They already exclude pre-existing conditions in many cases. Now they can deny you coverage for a disease you never had, but are slightly more predisposed to (assuming you get coverage in the first place)!
So this technology has the potential to significantly reduce coverage at a time when America is already suffering from too little coverage. The system has to change drastically before this technology becomes prevalent.
p.s. I didn't even address privacy concerns. Legally speaking, if you are covered through your employer, the plan's administrator is not allowed to discuss your health records with the employment decision makers (AFAIK, IANAL). But as someone pointed out to me, people talk off the record all the time...
p.p.s. If you haven't seen Michael Moore's Sicko, you really should, even if, like me, you don't like the guy. I prefer to debate based on the merits of an argument, not the person making them.