We can divide Feliciano's career into two pieces. Part 1 ran from from Pedro's MLB debut in 2002 through the end of 2007. Part 2 consists of the last three seasons, 2008 through 2010.
Pedro has been equally superb against lefties in both these parts of his career. Lefty hitters against him had a .575 OPS through 2007, and have had a .579 OPS against him from 2008 on. So no decline whatsoever against lefties.
Bu then we turn to Pedro against right-handed batters. In Part 1 of Feliciano's career, righty hitters had only a .727 OPS against him, a very good number for a lefty pitcher facing righties. However, from 2008 through the just-completed 2010 season, right-handed batters put up a .907 OPS against Feliciano. That is, the numbers indicate dramatic disintegration in his ability against righty hitter, albeit as with any relief pitcher's splits, we are not talking about huge samples, so it's possible Pedro's true talent against righties was not as good as the numbers suggest in Part 1 of his career and not as bad as the last three years' numbers indicate.
But if indeed the split numbers do reflect a real change in Pedro's true talent level against righties, and reflect the real magnitude of that change, Pedro can no longer be used to any significant degree against right-handed hitters. It would be sad to conclude that a fellow who was a full-service relief pitcher, and a famously prolific one, has declined into a pure "Left-Handed One-Out Guy". Unfortunately that may be where Pedro is at this point in his career.