Actually, this time of the year, Rafa isn't so bad. Obviously, he was absent last year and in 2009 he was returning from injury and wasn't his best, but in 2008 he won Canada and the Olympics, in 2010, he won the US Open, in 2011 he reached the final of the US Open. He's been in 2 semis and 2 finals (with one win) at the US Open in his last 4 visits.
In 2005-2007 he was still a kid, basically learning the HC game, though this gets held against him.
The time of the year where he doesn't seem too bothered in post-US Open, when he sojourns to China for the mega-bucks, and so forth, but rarely plays with as much intensity or urgency as he brings to his main bread and butter part of the year.
He tends to decelerate through the last couple of months, which is wise, given his intensity levels and knees...