This NeoGAF post has information on the apparent leak of the Mario Galaxy code well before the game's official release. It seems that the demo copies found at local Electronics Boutique stores only have a ten minute time limit when played on EB's proprietary demo machines, and when played in consumer Wiis, the disc actually contains the full version of Galaxy. Taking advantage of this, a scurvy EB employee lifted the disc, copied the data from it, and uploaded it all directly into the cargo hold of his nearest Internet receptacle.
While it is still not possible to download the data, burn it, and play it without certain black market modifications to one's Wii, such items aren't tremendously hard to find. While my desire to not be crushed under Reggie Fils-Aime's boulder-like fists prevent me from going into great detail on the subject, enough people know how to find these resources to make this news of great importance. I can't imagine Nintendo is very happy about this, but the cat is out of the bag, dressed as a bumblebee, and flying around the room regardless of what they do now.