The problem with it is that handguns for it tend to be made in the same size as handguns in 9mm. The result is that they are quite snappy in recoil, which (though not painful) can be disconcerting to all but the most high volume shooters.
One problem that arises with a snappy recoiling gun is that, unless you are really focused on a tight squeeze throughout your string of fire, the gun will shift a little in your grip, which will, after a few rounds, make you want to reacquire your grip. Most people would rather (1) not need to be focused to that degree on the squeeze of their grip, and (2) would rather not have to readjust their grip within a string of fire.
The solution would be to build a whole new size category of handgun for the .40 S&W, halfway (for example) between the size/weight of the Model 19 Glock and the Model 21 Glock, but that would defeat the original purpose of the .40 S&W, which was to have a power increase over 9mm in the same size/weight handgun.
