Several people, including many WoW Insider authors, have received Beta Opt-In keys for Wrath of the Lich King in the last 24 hours. This latest wave seems to be quite large. In previous waves I've known 1 or 2 people that have gotten in, where as this wave I know at least 16.
There is some speculation that this might be an attempt by Blizzard to thwart the release of Warhammer Online, which is set to come online next Thursday. Warhammer has received some mixed reviews, with many comparisons to World of Warcraft, including one by Michael Zenke of our sister site Massively.
Nonetheless, those that have received keys are enjoying the thrills of the beta. New levels, the Death Knight, and servers crashing a few times an hour. Good times had by all!