Skyrim DLC Announced 'Dawnguard'

So today the first Skyrim DLC has been announced with little more than a picture of the typical Helmed Nord with the word 'Dawnguard' underneath. Not much to go on, huh?
Something to take note of, however is the glowing eyes. Kind of reminds me of a Draugr personally except a yellow hue instead of blue.
Others have speculated that Dawnguard could have something to do with Dawnstar and its museum, especially the bit about the Mythic Dawn (remember them?).
One attentive player even found these files referring to snow elves (ancestors of the Falmer) and crossbows inside the Creation Kit.

So who knows what this DLC will be about. Considering Bethesda promised expansion pack-like DLC we should be able to expect quite a lot.