So what does this mean? One word: choke. Federer choked, and will continue to choke against Nadal. For how long? Until he doesn't anymore. For long enough that he's unlikely to win the French, ever. Early in Federer's career, David Nalbandian was his nemesis, a second stringer who consistently beat Federer -- sometimes beat him badly. And not because he was terribly talented, but because Federer would choke against him -- all the while beating top tier players like Roddick, Safin, Hewitt, and Agassi.
Anyhow, it took Federer years -- years of getting past a psychological block, analyzing Nalbandian's game, whatever -- to finally start consistently beating Nalbandian. He doesn't have years to break down the young Nadal, who has the potential to dominate the clay court like nobody since Borg*, who had won the French five times by the time he was Federer's age. Nadal is on that kind of pace.
That said, Federer can win. But he needs to play a clay court game. He needs to take advantage of the unbelievable angles he can put on the ball, his shot placement, and his strong, versitile serve. After the first set, none of those were on regular display on Sunday.
Sometimes players win matches, and sometimes the match is won for them. Nadal had the match won for him. Federer played awful tennis and gave away the victory.
*Of course, it goes without saying that Borg, the original ice-man, dominated nearly everything in his brief career. He won 11 majors in 8 years and went to an additional five major finals -- and retired at 26 (imagine Federer retiring next year, at 26). If he had been as good on hard courts as on grass and clay, it wouldn't even occur to people today that the "best ever" question was open for debate.