The important thing to remember is that results from a DNA test is just another piece of evidence. I think it is exciting in the limited cases where it works but it will never replace old-fashoned genealogy.
A DNA test without the written records is pretty meaningless. As a genealogist I want to know about my ancestors; where they lived, who they married, what they did for a living, and where they are buried. That comes from paper and microfilm.
On the other hand, this computer is very handy for sharing that written information with others. My computer is another tool I use.
And a DNA test can prove that two men are not related. That can be important in some cases. It is a tool that gives the right answer if the right question was asked.
DNA results only traces one line, the direct male line.
At 10 generations a person has 1,024 ancestors, half of them male. DNA can tell you about one of those men -- but not very much about him.