Here's the year by year average attendance for FBS over the past decade or so. One thing to note is the biggest of the bigs like Alabama, Texas, Ohio State, Michigan, et al, have more seats to sell than ever and have been selling them. It covers for major conference strugglers and the MAC/Sun Belt types that draw poorly by comparison and see a greater fluctuation depending on what happens on the field.
2001 - 44,068
2002 - 44,367
2003 - 45,447
2004 - 45,704
2005 - 46,039
2006 - 46,249
2007 - 46,962
2008 - 46,971
2009 - 46,281
2010 - 46,632
2011 - 46,074