The Late Innings: After losing Bobby Jenks and JJ Putz to the Red Sox and Diamondbacks, respectively, the Sox went out to sign Jesse Crain. Along with Matt Thornton, this group looks to be very solid. If Chris Sale is kept in the bullpen and repeats his dominance of 2010, this is among the best groups in baseball. Ozzie Guillen tends to like to play match-ups, so it is possible both Thornton/ Sale and Crain get the 9th inning instead of a set closer. In my opinion, this is the smart move, as whoever is most likely to get the outs needed should finish the game, not a guy in a set role. If the Sox can get by with Sale in the bullpen, and avoid curtailing his development, he makes Thornton the guy who can come in whenever, and get the desperation out.
Middle Relief: Sergio Santos and the recently signed Will Ohman make up this group, which can be considered very solid. Santos showed he may have closer potential, and had a very successful rookie year. He should be very good in his role. Ohman is a classic LOOGY, and is perfect for the likes of Joe Mauer and Justin Morneau (not to mention an enormous upgrade over Randy Williams). This, combined with the late inning core, has potential to reduce a game to six or seven innings.
Swing Men, Long Relief, etc.: Tony Pena showed last year that he can eat innings after a starter's disaster very well, and Lucas Harrell should be able to do the same. Clevelan Santeliz can also be considered part of this group, and will be used scarcely (think Scott Linebrink without the hefty contract). This group is nothing special, but, then again, what Major League team has a "special" long relief core?
All in all, this group should be one of the top in baseball. Though Jenks and Putz are gone, Crain and Sale should be just as good as they were. If Rafael Soriano's price were to drop, and Kenny Williams swooped in, it would likely give the Sox the best bullpen in baseball, but even without that happening, the Sox should have a very good bullpen.