We finally got a Wii. And, apparently, a broken copy of Mario Galaxy. Or maybe it's the Wii that's broken. Wii Sports plays, but while Mario Galaxy appears on the main menu, trying to load it results in a black screen for a while, followed by the less than helpful "An error has occurred". Cleaning it didn't help, and it didn't look scratched. I'll try it on a different Wii tomorrow and see what happens, but it sounds like it's 50/50 whether it's the game or the Wii that's broken.
In the meantime, our Wii friend code is [EDIT - removed, because we're probably going to get it replaced].
EDIT - Nope, make that a broken Wii. Mario Galaxy seems to work in the Wii here at work. Gah.