The online newsletter Genealogy in Time recently published an article that gave some warnings about unrealistic expectations concerning the accuracy of DNA testing for genealogy.
It makes interesting reading, and the best part of all is the conclusion that says "...you should become an informed consumer and make sure you understand the implications and limitations of such tests."
Perhaps it is the liberal use of DNA testing that we see in various police dramas on television that fools us into thinking that DNA testing for genealogy can be as precise in its results. Whatever the reason for that belief, it is not valid.
DNA testing is what it is...it is our expectations that try to make it into something it is not. Do your research before you invest in any test and be sure you know what you are getting and how to use it. The test results can be helpful or frustrating, and the difference is mostly a function of your own knowledge about the process.
You can see the Genealogy in Time article at http://tinyurl.com/379v7x8