I'm very excited to learn that the FDA has ordered 23andme to stop selling "personal genetic testing" to unsuspecting consumers. This is the company founded by the ex of Google's Sergei Brin (recent news here). So for a change, the FDA is doing something right for consumers, without waiting 10 or 15 years.
Here is a report on this action in San Jose Mercury (link). These tests have never been tested clinically and the company never applied for approval from the FDA. Given that it is not that hard to conduct proper testing of this product, especially if it is looking for diseases that have clear genetic markers, one suspects that the makers know that the tests would not pass rigorous testing.
There may be a day in which such tests are possible but the day hasn't arrived yet. I also think the chance that most diseases can be turned into equations that say if you have gene X, then you will develop disease Y is overly reductive.
One of the lesser studied effects of screening tests is the psychological impact of false results. If you tested positive for say breast cancer, and even if the biopsy showed the result was a false positive, there is always lagging doubt - every next time you feel something, part of your brain will make you worry. Then, there are those who take a better-safe-than-sorry attitude and elect to do procedures regardless - and some of these procedures have harmful side effects, which are frequently not properly explained.
PS. [12/3/2013] Andrew Gelman and readers join the discussion (link)