In case 100+ posts on this topic aren't enough, here are even more topics from the forum specifically discussing 9mm vs .40 for CCW:
http://thefiringline.com/forums/showthread.php?t=324542
http://thefiringline.com/forums/showthread.php?t=235041
http://thefiringline.com/forums/showthread.php?t=462024
http://thefiringline.com/forums/showthread.php?t=460796
I would have thought these would come up in a search to spare us another caliber war...