Correction: Federer ended Nadal's streak; he didn't end Nadal's dominance.
I agree with lil_brown_bat, Rafa is still dominant on clay. Also, while Roger was looking mighty dangerous in Hamburg, he has to win three sets in Roland Garros - very difficult against Nadal on a grueling clay surface. Nadal is one of the few players in the history of the sport that intimidates opponents purely through his level of effort and this is one the keys to his (continued) dominance on the red stuff. Personally, as much as I respect Federer I don't want to see him win the Grand Slam, I prefer it to remain a near impossible, almost quixotic, undertaking that escapes even all time greats like Roger.
PS. although I'm dying to see another Federer-Nadal final in the French, I'm even more interested to see if Rafa can put together another amazing tournament in Wimbledon and face off against Federer there. Last year I watched all of his matches at Wimbledon and after the barn burner in the first round, I've never seen a player maintain such incredible focus all the way through to the final - although he lost to the superior grass court player in the end, he won my undying respect with that tournament.
The idiots on the Australian TV coverage said that Federer only won because Hewitt took Nadal to 3 sets in the semi final, and therefore tired him out. Dear God.
All good things must come to an end. That will make the French that more appealing to watch....