It's anecdotal, and it's about transfer, not retention
This site says retention is down 11%:
http://www.dailyillini.com/media/paper736/news/2005/06/27/Opinions/Column.College.Chickenhawks-959410.shtml
I don't consider the site authoritative, though - I briefly looked for a better information source and didn't find anything one way or another.
