I know too many police officers who carry and like the .40 S&W. I think the .40 is here to stay, just like the .38 Special is here to stay. There are still some police officers who carry the .38 Special in a K frame revolver and that's a 100 year old ammo/gun combination but it still works.
Say what you will, Smith & Wesson knows how to do their homework when they introduce a new caliber. That's what nearly 160 years of experience can do for you.
I can see and appreciate the merits of the .40 but I don't own one and I don't think I need it. I would opt for either the big, heavy .45 ACP with medium ammo capacity or the high capacity 9mm with the smaller bullets but maybe I'm a traditionalist. After years of carrying a .38 snubby, I'm considering going back to the 9mm +P for the ammo capacity. I've seen too many carjacking and home invasion scenarios lately where lots of rounds were fired by both the criminals and the victims. I still plan on five or six rounds being more than enough to end a threat but just in case it isn't, I want to have 10 or 12 more chances. I've never heard of a gunfight survivor wishing to have fewer rounds in his or her gun but I have heard of panic setting in when the ammo is about to run out and there is no time to reload.
The .40 is a great caliber but in the 3rd generation Smiths for example, the 4006 is a 11+1 package in .40 S&W while the similarly sized 5906 is a 15+1 package in 9mm and it could go to 17+1 using Mec-Gar mags. That's up to six more rounds of ammo in the same basic format gun. Similar comparisons hold up with other brands. For example the Beretta is a 15+1 package in 9mm but the similarly sized Beretta 96 is a 12+1 package in .40 S&W.
We all hope that the extra rounds will never be needed but how many of us can really be sure? In reality you don't know exactly what you need until you need it.
Again, the .40 is a great round and it is here to stay but hey, 9mm +P is nothing to sneeze at, especially when using Rangers or Golden Sabers and especially when you can have more of them in your gun.