I went to Ed Demming's class on the use of DNA in genealogy last night. It was a good class with much to offer. The small class setting was ideal for asking questions and clarifying what is at best a confusing topic.
One of the crosses that the use of DNA in genealogy has to bear is the expectation that it can do more in identifying our ancestors than it really can. That mistaken perception is in part generated, I am sure, by TV mystery shows where DNA seems to give all the specific answers one could hope for. That may be the case in law enforcement where the task is to identify a specific person in connection with a crime, but it is not the case when the task is to trace ancestors back many generations. Ed's class did much to clarify that difference. That is definitely not to say that DNA testing is not valuable...it is. It is a unique tool that gives valuable information. It just doesn't give ALL the answers.
Karen Goldberg Goff, writing for The Washington Times, amplifies the points that Ed made in the class about the potential and the limits of DNA testing. Her article is a good one for understanding just what DNA testing can and cannot do for genealogists.
You can read her article at: http://www.washingtontimes.com/news/2009/mar/11/its-all-in-the-family/