Don't mess with Federer. After winning the US Open, Federer said "I'm not going to stop at 13. That would be terrible."
In Federer's "down" year of 2008, he only managed to make the semis at the Aussie Open, lose in the Finals at the French, barely lose in the Finals at Wimbledon... and win the US Open. Just wait until next year, when he's not dealing with the after-effects of mononucleosis!