Just received the "health" side of an ancestry.com DNA test.
Uniformly bland results, finding nothing which increases risk of anything (which is good, but they didn't cover the most significant area for me--Alzheimers--oh well).
The one correlation they did find is: increased likelihood of drinking coffee.
I'm rolling on the floor, laughing, since I've always drunk a lot of coffee. These days I'm down to about 5 cups a day, about 2 of which are leaded. I suspect if I had an obituary drafted by the group of people who have known me over the years, the lead sentence would be: "Bill drank a lot of coffee..."
(On a more serious note, I'd be curious to see some statistics on the percentage of tests for different things actually show a result exceeding the average. I suspect it's low, quite low, but because it's us and we worry about the bad stuff, a DNA test is an easy sell.)