Matheath,
Tough question for a man who has carried a concealed weapon of one sort or another for 30+ years, but generally speaking I guess the caliber I carry today is smaller than in the past. I currently carry 9mm most often (Kimber Tactical Pro II in 9mm and/or Taurus 905 9mm revolver), but in the past I have carried virtually every caliber from .22 through and including .44 mag and .45 acp. with a heavier emphasis on the larger calibers. The calibers I have carried have largely been dependent upon the circumstances of life. For example, when I started carrying as a young man, I started out (not surprisingly) with a .38 special/.357 revolver. After I became a lawyer and while handling a heavy divorce practice, I tended to carry .44 mag/.44 special/.45; when I moved to a corporate litigation/police defense practice, the caliber of carry became smaller (fewer death threats!). As I have aged, my caliber has diminished...it is easier to carry heavy when you are younger! And bullet construction has improved over the last 30 years making smaller calibers more effective than they were.
So, I guess I have gone up and down over the years, but have finally settled, at least for the time-being, on the 9mm, and I feel quite satisfied with the choice.
Boarhunter