For a interesting take on the depth and speed of the 2007 bear market in the S&P 500, here's a chart showing the index and the variance above and below the 12-month simple moving average (SMA).
Prior to this bear, since 1950 we experienced a 25% plus variance below the 12-month SMA for only one month in 1974. Last year the index dropped over 25% below this threshold for six consecutive months (Oct-08 to Mar-09). It finally moved into positive territory with the July close — up 5.1%.