I've heard from a few competitors in Torino that Yu-na Kim did not want to skate in these World Championships, but her federation told her that she had to take part. Of course, the short program problems she attributes to her left foot shaking, but may it actually be that she wasn't fully prepared and planned on just ending her season in Vancouver? Not that a silver medal is a bad thing (nor is winning the long program, obviously), but I'd imagine that if she just really got back into training seriously a week ago as she mentioned in an interview, that there might be some truth behind the gossip.
Yu-na has had a long year, and I'm sure it got even crazier after her Olympic gold medal. If she needed a break, she should have been allowed to have one. Not earning the World title in an Olympic year isn't the end of the world.