The fundamental premise behind all DNA testing companies is that buying their test will tell you what you would not have otherwise known. And the disappointing reality is that they are essentially out to bleed you with enticements as you search for the truth of your heritage. It is not rewarding to learn that the enormous data you're first offered when you begin with Ancestry.com will be snatched away after a trial period. In fact it's quite a nasty awakening. That company has limitless power and unceremoniously devours millions of sacred databases in its path. Like the graveyard records here in my village. Now they belong to Ancestry.com and we must pay to see them.
The programs you've seen on television are probably factual when journalists report discrepancies and inaccuracies in the data of paid DNA companies. I agree that if someone has tested bloodlines with a DNA company and there are few (or no) others among his/her bloodlines registered in the database, it is ludicrous to think that information will surface about known relatives from close generations. Your DNA will, however, fetch you some centuries-old probabilities about your continental origins and so forth. This might be interesting, but I doubt that it's the focus for many of us.
I personally want to know about people in my immediate past. Let's say the past 100 years. Those are the people who matter. Whether my distant ancestors (might have) travelled the seas of Mesopotamia 3,000 years ago is not what I came for. When my father hung around B'ham, he was among thousands of young Canadians during the war. I need not say more about the probabilities, but I'd be absolutely fascinated to learn that I have British relatives. In fact I don't doubt for a millisecond that by this point in history there are tens of thousands of Brummies who are related unwittingly to N. Americans in the aftermath of WW2. Sorry if I offend, but that is just a reality that cannot be erased.
The analysis of your blood, if a DNA company's employee is cautious and scrupulous, is a wonderful thing. It has already helped millions of people find relatives (me included) who might have been given up for adoption or whose significance to family heritage fell by the wayside in past generations. It's the very thing that should make everyone pay attention to the technology.