2005 -- 34.73%
2006 -- 34.94%
2007 -- 35.04%
2008 -- 35.23%
2009 -- 34.40%
Change was made at end of 2007 season, so impact would seem to be negligible.
Number of attempts hasn't changed much, either. 2008 was the record year for number of attempts, but I'm not sure that's statistically significant (and it's certainly contrary to expectations).
2005 -- 18.33 per game
2006 -- 18.43
2007 -- 18.89
2008 -- 19.07
2009 -- 18.33
Source for stats: http://web1.ncaa.org/web_files/stats...ds%20chart.pdf