Olderer being old again.
EDIT: Man, Federer's RoS is so bad these days. I mean, it was never the best on tour, but I mean damn. That was just tragic. Beaten by the world 114 who has barely even played outside challengers before.
EDIT2: I think half of the problem isn't just Federer's play, it's the fact that,as Stahkovksy said, people are playing him and his ego but these days his ego just doesn't cut it. Delbonis was so solid, never choked, consistently going for fearless shots. In the old days, guys often used to look like they'd given up already when they started a match with Federer, and if your opponent isn't confident you can easily run away with things even if you are having a bad day. Now, bad days end up with Federer losing.