If you have seen Who Do You Think You Are you have seen what you can learn from Autosomal DNA testing. What comes to mind is Vanessa Williams and the fact that she has Italian DNA.
The genes that are tested are not the same ones that are used in other tests but if you are curious about what your ethnic makeup is, this test can give you a lot of information. One thing that is curious in this test is that siblings may be quite different in their results. My brothers and I certainly are. They are much more Irish than me and I am more Northern European.
I am not sure if I understand it correctly but to my way of thinking it is how your actual ethnicity plays out in you. I have brown hair and brown eyes and my brothers have blue eyes and dark blond hair. We obviously did not get all the same genetic makeup.
There are several different companies who offer this test and they will also tell you who among their database is related to you and an estimate of the degree of relationship. If you are looking for family connection this can be a big help.
I did this more for the entertainment value and it definitely has provided that. If you have always wondered if you really have Native American blood or if those stories in your family are true, this is one way you may be able to answer those questions.
But having said that, my Mito is Native American and the only thing remotely odd in my Autosomal DNA is less than 1 percent Finnish /Western Russian. My brother has the Caucasus so I am not quite sure what to make of that. He also has Greek and Italian which is missing from me.