I got a launch wii, and it the graphic artifacts within weeks... within a couple of months i had it covered in artifacts, even on the menu screens. I put up with it for six months so i could just screw the guts out of it before i got it replaced. Basically kept in for 10 months then got it replaced by nintendo. Only took 10 days to send it off and get it back. The other guy i lived with got his at launch too and it had the same problem.
Now I've had my replacement since about october and not had a single problem with it. I turn it off at night is all i do and it gets used at least 6hrs per day for games and youtube... no probs at all, solid as a rock!
I have this feeling that Nintendo made all the euro consoles and discovered they had a faulty batch and decided to ship that lot to australia, because we don't really count compared to europe, especially at launch. That way they could still deliver a batch of faulty units to the ass-end of the earth where it wouldn't get major media coverage. I dunno, just a theory. But over many message boards for the couple of months after launch i read alot of posts regarding this issue here in oz.
Anyway, like i said my replacement is still like new after 6 months of heavy use and no probs.