A New York Times article published today
noted how Davydenko "is consistently among the best on the ATP Tour in percentage of points won off opponents’ first serves. He has the feel, flexibility, footwork and anticipation that are the distinguishing characteristics of the best returners. This year, the most universal of tools has forsaken him. Since Davydenko switched racket manufacturers, he said, his return has not been the same."
I looked up his stats vs. Federer to see if he ever kept Federer's success on first serve low enough to fall below success on second. It happened once, but actually Davydenko is the one more often who has higher success on second serve.
Federer – 72% on first, 76% on second, d. Davydenko, 2005 Doha
Davydenko – 65% first, 66% second, lost to Federer, 2005 Rotterdam
Davydenko – 56% first, 58% second, lost to Federer, 2005 Hamburg
Davydenko – 51% first, 60% second, lost to Federer, 2006 USO
Davydenko – 53% first, 60% second, lost to Federer, 2010 Cincinnati