Thanks to JD2020, the community manager of Treyarch, for the info, posted originally on the Call of Duty homepage.
We’ve decided to celebrate the successful launch of this update with Double-XP Multiplayer! This coming weekend (March 6th – 8th) all players will accrue 2x their normal XP in all playlists – on ALL supported platforms! This includes Xbox 360, PLAYSTATION 3, PC, and the Nintendo Wii.
Be sure to clear some room on your calendars, as it’s going to be a frag-filled weekend indeed. The action starts Friday morning, and ends Monday morning Pacific Standard Time – see you online!