Kotaku just posted an article discussing several things from Dawnguard here: http://kotaku.com/5916595/skyrims-massive-dawnguard-sounds-like-a-proper-old+school-rpg-expansion
The highlights; The DLC adds two new "huge" landmasses to explore, as well as a large amount of base content to the game.
The Dawnguard side of the story alone is 10-20 hours.
Not a whole lot of new info, but this is certainly a great DLC. I'm sick of companies scamming us with crappy little '10 new ingame items' for $10 and crap like that. This is a huge amount of content, and it's only for $20. Great work Bethesda!
