Announced at Quakecon: Dawnguard is now available for download on Steam. Read more on the BethBlog. This is actually very much Breaking News, not even SkyrimNexus has it on the front page yet, peeps.
Good news coming as a total surprise. Too late this evening for me and I just returned from a long road trip to the land where the sun never sets, so I need to sleep, but it seems I have my weekend cut-out.