Mike Fast has a splendid article on Ryan Vogelsong up on Baseball Prospectus. I highly recommend that you read it. This one doesn't even require a subscription to view.

An excerpt:

Once Vogelsong took hold of that rotation spot, he didn’t let go. Nine starts later, his ERA stands at 1.81, a mark bested only by Josh Johnson at 1.64 and Johnny Cueto at 1.68, and ahead of the leader among official qualifiers, Jered Weaver, whose ERA is 2.06.

Vogelsong’s performance this year is all the more surprising because he entered the year with a 5.86 career ERA, compiled in 315 innings pitched for the Giants and Pirates from 2000 to 2006, as described in John Perrotto’s article last week. He spent the 2007-2009 seasons in Japan and returned to the United States for the 2010 season, hoping to catch on with the Phillies but being sent to the minors instead. His performance in the minors in 2010 was not particularly stellar. How is it, then, that Vogelsong has been among the best pitchers in the league in 2011?

He proceeds to break down the PITCHf/x and batted ball details. The conclusion that he comes to bodes well for the Giants chances to repeat. "The pitcher who produced that 5.86 ERA five years ago appears to be gone, replaced by one who knows how to use his stuff to good effect."