Warhammer fan sites Rainbow MMO, Asuryan's Flames and Epic Slanta received greeting cards with not-so-subtle hint at something happening in the second week of February, and many speculate it's the Dark Elves holiday: the 'Death Night':

I got a heartwarming greeting card from Dimpled Bear! Err... well, ok, maybe it wasn't exactly from WAR's lead Bear Creative Director, but still!

It seems to be a not-so-subtle hint at an upcoming Live Event based on Valentine's day. Is this a tie in to the release of the Slayer/Choppa classes? That would certainly go along with the blood spattered cards (which are super cool, by the way!). But what's going on with the "which elf" and the black kisses? Seems to indicate the Witch Elf class could play heavily into this event, and it definitely looks RVR based (Huzzah!).

I know others have gotten these, so let me know if you have. Werit and Keen have theirs up now, so check them out. I noticed Keen's is 9/13 (lucky number 13?) and has a "V" under the numbering. Mine is 4/13 with an "I."

Guess away kids!

UPDATE: Asuryan's Flames and Epic Slant have theirs up too... it's getting interestinger and interestinger.... Both of their's mention Squig Herder's and the Night of Murder. Also, Epic Slant's is 6/13 and "7"

UPDATE 2: Wizards & Wenches has a good guess as to what we might expect:

DEATH NIGHT

The official "holiday" for Dark Elves in general, but Witch Elves and Disciple of Khaine in particular. Straight from Wikipedia:

The holiest time of the year for Dark Elves is Death Night. During this night the Witch Elves rule the streets of the Dark Elf cities, capturing anyone they find (whether they are slaves or Dark Elves) and dragging them back to the temples as sacrifice to Khaine. The Witch Elves will even go so far as to break into houses, which has led to Dark Elf families barricading windows and doors during this night. On Death Night, the Witch Elves will also steal away a number of children. Girls captured like this will be trained to become Witch Elves. Boys are tossed in a cauldron of boiling blood. Those that survive are trained to be true adepts of Khaine: the feared assassins. As dawn breaks after Death Night, it is customary for those who lived through the night to make a sacrifice from their own household (usually a favoured slave or elderly relative) as a thanks to the Lord of Murder for sparing their family.

Source