DVR penetration increased by about 4% in the last year on an absolute basis (11% on a relative basis) rising from 35.7% of TV households with DVRs in February 2010 to 39.7% in February 2011 according to Nielsen data via Turner's research department. The percentage of viewers reached in those DVR homes rose from 38.5% in February 2010 to 42.2% in 2011. As you can see below, the landscape was very different in February '07, though many complained that the DVR percentage was too small in 2007. The single biggest increases came for the 2007-08 season (not listed below, because I don't have February data) when Nielsen bumped it up to around 25%.
Feb 2007: 01/29/2007 - 02/25/2007; Feb 2010: 02/01/2010 - 02/28/2010; Feb 2011: 01/31/2011 - 02/27/2011