Valve are set to release a free Portal 2 DLC pack dubbed "Perpetual Testing Initiative" for PC and Mac which is due to hit on May 8. Valve have said you'll be able to "easily create, share, and play Portal 2 puzzles" with the new DLC.
The new level creator will let you publish maps directly to Steam. Yes! Other players from there, will be able to browse, vote, and download user-created maps to play in their own versions of the game.
There's not much more on this until May 8, but you can sure it will be featured as our Download of the Day.