Getting away from the medical angle of DNA testing, I’m not sure if I mentioned here that I got an interesting result from Ancestry.com.
I knew that all my grandparents were Jewish and immigrated from Russia. So the result I got had one small aberration, but one I didn’t think much about:

I’m talking about the blob over the British Isles.
I had always wondered if I was adopted - none of my relatives are tall, had curly blond hair as a child, or blue eyes.
Long story short - I was contacted by a lady who said her husband and I were either siblings or very close cousins. They also live in Georgia and we met, and had a lot in common. So far, it seems as though I share a father - not the one who raised me - with at least 3 other males and 3 other females. All of whom were born in Washington, DC between 1947 and 1955 to mothers who were having trouble conceiving. Speaking to another descendant led to a gentleman of Scottish descent in Washington, DC, who was a medical student and almost certainly the common sperm donor to at least the 6 “siblings” so far discovered. A living aunt confirmed that my mom had had trouble conceiving and had finally gotten pregnant after a “procedure”.
Just pointing out you never know what your DNA might show if you take the leap and have it checked!