Since its release on the PC and Mac in May, 2012, community map makers have used the Steam Workshop and Portal 2's in-game editor - called the Perpetual Testing Initiative - to create and share more than 170,000 single-player test chambers. With this update, the community will for the first time be able to design puzzles that require two players working cooperatively to solve.
This update also introduces a "Quick Play" feature, which allows players to quickly access the top-rated maps in various categories.
To help players find a co-op partner, Valve is giving every current owner of Portal 2 a Steam coupon for 75% off a copy of Portal 2, which can be given away to other Steam users.
Sounds great, just need to find some friends to play with now.