In an interview with David Sawyer, a key figure behind shipping the Puzzle Creator, he revealed that Portal 2 has sold over 4 million copies worldwide. As with many Valve games, the company sees increased sales during period of price drops (66% off now!) or new content being made available so that figure is likely to only rise more on the back of today's release of the PeTI DLC.
He also revealed more DLC could be still be coming out for Portal 2, now over a year old, with more content.
Meanwhile we've been keeping an eye on the good work being done by the Puzzle Creator users in the multiverse. I imagine Cave Johnson has a similiar opinion as Revenant100 who produced the map below.