Take a look at the Wrath of the Lich King beta patch notes after the break. WoW Insider believes these to be the real thing. With the activation of the beta downloader and beta site, it seems like there is quite a bit of activity at Blizzard tonight. Expect to hear more as the night goes on.
If you haven't signed up for the beta yet and wish to do so, you can head over to the beta opt-in page and make your intentions know to Blizzard. It is rumored that the first round of invites will begin shortly, and we're all waiting on pins and needles for the emails.
Additionally, any information gained through the beta does not have an NDA attached to it, so expect to see a lot more information in the hours and days ahead.