So I was given a beta key last night (yay!) Big thanks to the guy who got it for me!
I only got a chance to play around for a couple of hours but things are looking great so far, both for Warlocks and Deathknights.
I did throw up some initial feedback on the beta forum, however. Check it out here.
Let me know if you guys have any questions in particular about Warlocks or Deathknights and I'll try to answer them if I can!