Valve today announced a new piece of DLC coming to Portal 2 on May 8, one designed to let players craft their own puzzles. The Perpetual Testing Initiative is a "simplified" puzzle maker that allows players to create their own puzzles and directly publish them to the Steam Workshop, where other players can download and rate them.
The DLC will be a free download for PC and Mac users. Unfortunately, it doesn't look as though console players will be getting this content, though based on previous history, that's not too surprising.
While I haven't touched Portal 2 since the last DLC came and went, I have to admit the possibility of downloading some new user-made puzzles has me itching to fire the game back up again. And I'm sure once the whole thing degenerates into people making nothing but cake-related joke levels, I'll stop again. But the time in-between should be fantastic.