Great stuff via Neil Paine:
The 2010 Yankees-Twins ALDS represents just the 8th time in the WS era (1903-2010) that the same two teams faced each other in a postseason series 4 times in 8 seasons… The Dodgers & Yankees played each other in 4 world series from 1946-53, 48-55, and five times (!!!) from 1949-56. The Yankees and Royals faced off in 4 series from 1973-80, and the Braves & Astros had two different 8-year stretches with 4 playoff showdowns in the late nineties/early 2000s (1997-04 and 1998-05). The Red Sox and Angels capped off a 4-series-in-8-years stretch last season, and now the Yankees and Twins have joined that group with ALDS faceoffs in 2003, 2004, 2009, and 2010.