I won't get a .40 caliber Glock - not because of KaBooms, not because I hate the Glock, but I have a minor grudge against the .40 S&W.
9mm Parabellum, 10mm Auto, .357 SIG, .45 ACP, even the friggin' .45 GAP (oh, to try out a .380 Model 25).
In the past, I told myself it was because the .40 usurped cartridges like the .41 Action Express and the 10mm Auto, but the .357 SIG steps on the .38 Super's toes, and the same applies to the .45 GAP for the .45 ACP.
I think the reasoning is because it stepped on both the 9mm AND the .45 ACP. The compromise round between the two offends my "if I can't pack a 9mm, I want a .45" sensibilities.