Mine is modded with the wiikey and I am playing Metroid prime 3 which I downloaded from torrentspy.com.
So man IT WORKS. When I put the disk it it ask to be updated I did and the game starts and no trouble. I also have fifa soccer 08 and I am playing that online also with no problems. I have been kicking some English arses like every night.
If u have the wii key then you will be ok. As for Mario Galaxy, the wii key already have the update that will work with it. So don't worry.