Gee Jay-again, I'll preface what I know on DNA testing thru Family Tree and Ancestry. My husband has gone thru both the Y and the mitochondrial. Again, his background is mainly Scottish/Irish with a little German scattered in there. He has helped a number of people thru their searching. The Family Tree DNA will give you generalities (like Eastern European, Scottish/Irish) but the best part in his opinion is pointing you to others who are searching for either a similar family name or group. This can either help confirm your own research or give you other leads to those who can help. Think of the results as either a pointer or additional guidance for your search.
The pointers can be a huge help-most of us in this forum have solid proof of where our families came from (at least as far as country) but the biggest brick wall is the variations on name spellings. I finally found some basic information on my Grandmother and her first husband under one of the most contorted spellings of the last name that I have found to date. In cases like this, the pointer to someone researching a similar group can be a huge help.
My husband had a gentleman call him several years ago. This person told my husband that he had gone thru the Family Tree testing and it lead him to my husband who was researching similar names/family groups. With some help, they both came to the conclusion that in a distant connection, they were both related but apparently there was a slight parental surprise for the man who contacted my husband. As many dyed in the wool Southerners will tell you, "If you don't think there's a Yankee in the wood pile, you're either lying or fooling yourself!" Good Luck!