As you can see above, Blood Elves and Humans dominate the race choice in our little group, which seems about right, considering that those are the two most popular races overall. Death Knight players in this study generally tend to have reported themselves as male in real life. And GamerDNA also lays their Death Knights up against the Bartle test and while WoW players trend pretty well to the norm, Death Knights go way more towards the "Killer" and to a lesser extent the "Explorer" end of the scales.
So according to this little survey (and we'll remind you that this is 500 people, so there are plenty of exceptions out there), the average Death Knight is male, chooses whatever race is most familiar to them, and wants to go kill and do damage rather than worry about socializing or achieving. In other words, lots and lots of former Ret Paladins. It'll be interesting to see how this changes over time -- lots of these players are interested in the newest thing, obviously, since they've switched their mains to a new class at the first chance, but as things settle down and more people head back to get new alts, maybe we'll see a different crowd coming out of Acherus.