During the 2010-11 offseason, 42 relievers signed Major League free agent deals. From Rafael Soriano at $35MM to Taylor Buchholz at $600K, almost $253MM was invested in these relievers. How are they doing so far?
Numbers for the average American League reliever: a 3.86 ERA, 7.3 K/9, 3.8 BB/9, and 0.88 HR/9. AL teams threw around much of the relief cash during the offseason, accounting for more than 81% of the total spend. The 26 signees have totaled 576 1/3 innings, from Joel Peralta at 33 1/3 to Pedro Feliciano at zero. The average reliever in this group has 22 innings. The results for the free agents: a 4.09 ERA, 7.6 K/9, 3.5 BB/9, and 1.00 HR/9 - pretty close to league average. Though he's allowed five home runs, Koji Uehara has probably been the best investment.
The average National League reliever has a 3.54 ERA, 8.0 K/9, 3.8 BB/9, and 0.74 HR/9. NL teams invested only $48MM in relievers, as compared to $204MM for the AL. The 16 NL signees have totaled 306 1/3 innings, or about 19 each. Chad Qualls has been the workhorse at 35 innings, while Takashi Saito has registered only two frames. As a whole the group has a 3.64 ERA, 7.8 K/9, 3.3 BB/9, and 0.85 HR/9, also pretty close to league average. With almost everyone in the group costing $5.5MM or less in total, there are plenty of bargains such as Qualls, Randy Choate, Todd Coffey, George Sherrill, and Buchholz (though he's currently injured).
My apologies for the lack of a groundbreaking conclusion here. The 2010-11 free agent relief class has performed around league average. The American League's heavy spending (36% of which came from the Yankees) has not paid off when compared to the National League bargain shopping.