Yes you heard me correctly! You can now make Co-Op maps from the puzzle maker. Download maps from workshop and invite a friend. The friend will also automatically download the test and you will be able to play it together!!!!! All puzzle elements are of course supported. Furthermore, all current owners of the game get a free 75% off coupon so they can send it to a friend who doesn't have the game yet!!!! Here is the full blog post
http://thinkwithportals.com/blog.php