Maybe, but for most of the season the Packers' D was among the best in the league. In fact, according to Football Outsiders, Green Bay ranked second to the Jets in total defense during the 2009 regular season (third against the rush, sixth against the pass).
Of course, you wouldn't have known that watching them against the Cardinals and Kurt Warner last weekend (or the Steelers last month). But here's a little something for the glass-half-full set: in 2008, with a fully functional Bob Sanders as the defensive coordinator, the Packers had the 12th-ranked overall defense (seventh against the pass, 28th against the rush).
If Capers can successfully transform this unit from a 4-3 liability to a 3-4 dynamo (for 7/8th of the regular season, anyway) and still squeeze in a few naps during games, what does that say about Sanders' coaching skills?
As for Capers, just have one of the equipment guys spike his Ensure with some Red Bull. imagine how good this defense will be if he can manage to stay awake for four consecutive quarters.