According to my EB contact the failure rate of XBOX360 in Australia (according to what he sees returned) is about 15% - 25%. What I really laughed about is he thinks this is good as its much better than the redesigned Sony PS2 (apparently lots of laser tracking problems initially), and is on par with new console releases.
He did admit the GCN is very reliable, he has only seen a few returns mostly for a stuck power button (I actually had this problem).