I already knew my family history well enough for me, there were no surprises. Going back the previous 4 generations was exactly as I believed it would be. I had a long struggle with myself over possibly becoming the next Henrietta Lacks and my typical privacy concerns but finally decided I wanted the health screenings offered by 23 & Me. If it was the ancestry information I wanted, I would have gone with Ancestry.com.
One of my on-going health concerns was a too-high blood iron level, well it turns out I have one gene that tends towards that, if I had two I'd be having more problems but as it is, it's ok with one, not such a concern any more now that we know (and it was retested). The amount of insomnia information wasn't what I had hoped for, but yes -- indications are that I would tend to sleep less than most people.
Like another poster, I do have more neanderthal genes than most people. And I'm related to Otzi the Iceman through my mitochondrial (maternal line) DNA.
My son's dad doesn't know much of his family history past his maternal grandparents and basically nothing about his father's side at all, and pretty much all of his relatives have died out. I've been thinking of getting him a kit and maybe one each for my son and daughter in law. Similarly, my husband actually knows a bit about his father's side of the family but not much past his maternal grandparents and nothing is written down.