From October 29 until November 2, experience points earned throughout all of the multiplayer modes found in Gears of War 2 "skyrockets" to 31 times the usual amount.
Epic is also "shaking things up" with a special "Chainsaw Massacre" edition of the game's popular Horde mode. "Lancer-only matches with no more chainsaw interrupts to save your enemies (or you!) from certain gory evisceration," a blog post on the game's official site reads.
I haven't played Gears of War 2 in ages but at an XP bonus of 31 times the normal rate? I think it's time to dust off that chainsaw and shoot for some missing achievements.
[Thanks for the tip, Jeff]