it's amazing to me how often this debate comes up. and of course, there are those who say the 9mm is horrible, and if you don't have a .45, you might as well be throwing rocks at an attacker. some rely on the numbers approach -- amount of penetration, energy, velocity, etc.
the funniest part to me is, this has all been discussed at length over at tacticalforums ... here's a link to the topic i'm referring to:
Service Pistol Calibers. please, before you make a boisterous comment to the effect of a .45 knocking a man off his feet while a 9mm is akin to barely stabbing him with some tweezers, read the posts there <img src="/images/graemlins/wink.gif" alt="" />