Last year I had my DNA tested by Family Tree DNA. I was mainly interested in their autosomal test, but I also ordered a Y-chromosome test just to be thorough. This proved to be a good move, because the test revealed some awesome things about my direct-line paternal ancestors.
The findings can be broken up very roughly by time-period.
Recent History (the last 500 years)
My main goal in taking the Y-DNA test was to find people who share my surname. I was hoping to compare notes and maybe find out where our line originated. My own Moyer/Meyer ancestors have been in America since 1750 at least, and I can't trace them back to Germany, so having another line of descent to trace would be very useful. Surnames in Europe stretch back about 500 years, so a Y-match sharing my name would be, at most, my 18th-or-so cousin.
As it turns out, my closest match was indeed a Meier. I wrote him and eagerly awaited a reply. Sadly, he never responded, a problem that plagues DNA testing sites. Luckily he had posted enough about himself that I was able to cobble together his family tree. I traced his line back to Henry Meier, a prominent businessman in St. Louis. Henry died in 1900, and I was able to locate an extensive obituary that gave his place of birth: the province of Hanover, Germany. This doesn't necessarily mean that my Meyer ancestors were from the same place, but it at least provides a starting place.
Middle History (the last 1,000 years)
What else can we tell from the Y-DNA test? Well, one fact that jumped out at me immediately is that, save the one already mentioned, every single one of my matches traced their ancestry to England, not Germany.
This result strongly implies that my paternal line spent quite awhile romping through the British Isles before packing up and moving to the Continent. It's even conceivable that the traveler already had the name Meyer, since the name is English as well as German.
I hope to eventually confer with most of these matches to see if there is a particular region of England where they cluster. However our common ancestors are so remote that the various lines probably had time to spread all over England.
Remote History (4,000 to 5,000 years ago)
This last result is what most people expect from a Y-DNA test: their haplogroup. Mine happens to be I1. This group has a high concentration across Northern Europe, maxing out in southern Scandanavia. There is some disagreement as to where this haplogroup originated, but I believe the most recent thinking suggests Denmark.
In Great Britain today, the I1 haplogroup appears more often on the eastern side of the island, so that's likely the general area my ancestors inhabited while in England.
Putting it Together
When taken collectively, this really offers a compelling picture of my paternal ancestry. The story begins somewhere around Denmark while the pharaohs were building their pyramids in Egypt. There, a man belonging to the I1 haplogroup begat a son, who begat another son, and so on.
Eventually, an x-great grandson traveled from continental Europe to England, which has seen influxes of Germanic peoples throughout its history. In England, the sons continued having sons, until one day, one of those sons went back to the continent, and possibly settled in northern Germany. More sons and more sons, until finally, one of them packed up, got on a boat, and came to America. In Pennsylvania, they had more sons: Wilhelm, Peter, Peter, Nathan, Roger, Alfred, David. And finally me.