I have tested myself, both my parents, and my maternal grandmother. I am hoping to get more of my grandparents on board.
When I first got my results, I was surprised to see 24% Irish, as I have only found one Irish ancestress who lived long ago. All my identifiable ancestors from present day UK were English or Scottish. I'd originally assumed my British percentage would be much higher (It's less than 1%).
I also didn't quite expect the 20% Scandinavian. I'd expected to be mostly Eastern European (which I am, at 44%) and Western European (which ended up only being 9%). Now that I understand ethnicity results better, I don't take much stock in it.
Ethnicity wise, it was a surprise to see some African on my mother's DNA results. After seeing her mother's results and doing some DNA phasing on GEDMatch, I believe this is on her father's side. Definitely a surprise.
The other thing I got from my DNA results wasn't necessarily a surprise but a correction. My second great grandfather had a mystery mother. After being given his birth certificate, I finally had her name, age, and birthplace. I found a woman who fit this exact description and of course assumed her to be my 3rd great grandmother (maiden name Hoover, from Dayton, OH). After taking a close look at my matches, I saw someone who was a fairly close match and had ancestors named Hooven from Dayton. I looked into it on a whim and found ANOTHER woman named Nettie HooveN (not HooveR), same birthdate, birthplace, etc. I ended up being able to figure out that this Nettie Hooven was my actual ancestor, all from DNA. I'm still quite pleasantly surprised that I was able to do this.
My grandfather's grandmother was adopted, so I'm still hoping something will pop up to help me learn more about her origins and/or family.