Anyone done a DNA test and learned something interesting?

no way! thats amazing, congrats! Tbh that was my hope too, to find a relative but no such luck on my side...

Found out that my very Italian grandmother is actually a good 30 percent Middle Eastern! (Unfortunately the test isn’t more specific than that.) Which just makes me even more of (to quote a former editor) an “all-American mutt”! 

I learned my dog is seven different breeds.

Depends on what you mean by "trace." If you take the test (which with Ancestry.com basically consists of drooling/spitting into a tube and sending said tube to them--yes, I know, that's icky), they will do a lot of the initial work--i.e., telling you what your national/ethnic genetic background roughly consists of, along with approximate percentages of each strain. Of course, it isn't free of charge, but by paying their fees, you will be provided access to many records that would probably be closed (or much less accessible) to independent ancestor-seekers. And they will anonymously and privately suggest possible relatives (e.g., "You have a potential third cousin").

In my case, it wasn't so much that I learned something new as that Ancestry.com confirmed that what I was told by my parents was largely true (and not just family legends). For instance, I had always been told by my father that his father (the grandfather I never knew) came over from Scotland in the early 1900's. Not only was that confirmed, but I also found out that my maternal great-grandmother was indeed of Welsh descent, as my mother's family always maintained. I also discovered that, in addition to many, many Scottish forebears (on both sides), I had quite a few who were Sassenach--er, English. And, getting back to my father's side, I had confirmation that his grandmother--not the mother of the father from Scotland--was born in Ireland.

So what with the Scots, the Welsh, and the Irish, I'm as Celtic as I believed--and hoped--myself to be (with the aforementioned English thrown in for good measure). Plus, I had a tiny sprinkling of French and Dutch ancestors as well, with the most exotic strain being a trace of Finnish.

One disappointment: because my maternal grandfather (a Missouri-born college professor) had high cheekbones and straight black hair--that is, when he still had hair --I always hoped he was of partial Native American descent. Nope. Same old British Isles ancestry. Oh, well. But then, as the Scottish saying goes, "We're all Jock Tamson's bairns." (I.e., "children of Adam.")

I know my heritage, and I have no interest in sending my DNA to any random lab so they can have it on file for some random data base. I've never understood the fascination with anyone wanting to find this stuff out.

What difference does it make? You're still you. What difference will it possibly make to how you live your life, finding out this new information? You're really going to go change your lifestyle or perception of your existence based on a test?

Worse yet, digging up some completely random potential relative who may or may not want anything to do with meeting you? Why would you do that and disrupt someone else's life out of your curiosity?

To what end?