A little historical perspective courtesy of Jim Geraghty and Charlie Cook:
Cook Political Report from September 1, 2006: 35 GOP House seats rated as Lean or Toss Up; 9 Democrat House seats rated Lean or Toss Up.
Actual swing in November: 31 Democrat challengers beat GOP incumbents or won open seat races; no GOP challengers beat any Democrat incumbents.
Cook Political Report from September 2, 2010: 73 Democrat-held seats are rated as Lean or Toss Up; 8 GOP House seats are rated Lean or Toss Up.
