Apparently, my CC0 art was used in a real game.

Life Of Pixel, a PS Vita platforming game that runs the player through levels inspired by different console and home computer games, has a few NES-style levels based on my OpenGameArt submissions. From the screenshots on the page, the level "Shinoobi-Doobi" uses my city set -- along with the layout, while "Haunted Mansion" uses the castle set as the background.

BrightRetro seem to have participated in creating pixel art for the game -- and to be fair, they are also uploading some awesome stuff onto OGA themselves, distributing it under CC-BY.