The Portal 2 team just released what they're calling the "Perpetual Testing Initiative," which allows you to easily create, share, and play Portal 2 puzzles. This update to Portal 2 comes with a simplified Puzzle Maker which allows that creation of mind-bending puzzles without ever leaving the game.
The Puzzle Maker publishes maps directly to the Steam Workshop where you can browse, rate, and subscribe to ones you'd like to play. Subscribed puzzles will automatically be downloaded and installed inside Portal 2.
Just a couple hours after release, the Workshop for Portal 2 is nearing 4,000 maps for you to explore and test out.