An interesting question sir (tips my hat). Make my vote a +2 with Mr. Camp and Mr. Erich (and most of the other folks who have responded).
To be honest I was a big 10mm fan, and carried first a Colt Delta Elite at work as my primary. When my agency killed single actions, I converted to a S&W 1006. It was hard for me to find either a factory round or reload my 10s did not seem to like. So I did sort of resent how the FBI trashed the 10mm, as I had some inside information and understood what was really going on there. It was not the pistol, nor the ammo. Rather it was a round the FBI was having loaded to their specs by two companies. Both companies and Smith tried to convince my illustrious brothers in arms that their specified load was simply too light to reliably operate the platform. An increase of 40fps in the loads would make the pistols 110%. But since my cohorts in crime knew far better than anyone else, they chose to trash the pistol/caliber and revert to a different round.
Smith actually developed the 40S&W in response as sort of a polite way of showing them, see this is really what you wanted, you just did not know it. So what does the Bureau issue these days? Would you believe a Glock in 40, lol. (No we do not swap spit in case you had not figured that one out, but I try to be polite when discussing them anyway.)
My first venture into the 40 was very early on, and to be honest I was simply not that impressed with it. I put it aside for a few years, went back to my two P226s in 9mm and was fairly content, although a bigger round suits me better honestly. When we changed the 40 round we issued for those who elected to carry a personally owned 40, I gave it another try on the range one day.
Maybe I was just more mellow about the round then, or maybe the ammo folks had simply gotten it a bit better too, but I shot the different round much better that day. I had a couple of other instructors shoot my 4006 and we all agreed something was different then. I sold the 4006 to a co-worker who shot it that day and just had to have it. I bought two P226s in 40, and they became my carry pistols at that point.
I currently have 4 pistols in 40S&W - a P226 on a steel frame, a 229, an FN HP, and a 75B. I find the accuracy in all 4 to be more than acceptable for carry purposes. As Mr. Camp noted, I do think the 75B is a bit more user friendly with the ammo it likes, as I have simply not found a poor combo for it yet, be it factory or reloads. But I can say the same about my 226 and to a lesser degree the 229. To be honest I only bought the 229 when an odd firearms policy would allow me to carry a personally owned 229 at work again, but not a 226. That was subsequently changed to allow the 226 again as well. So once I could go with a 226, the 229 does not get fired much, as I am simply not an alloy frame person really. Eventually I will probably sell it or trade it for another steel framed 226. But I could end up with a 229 in steel as Sig now offers that version too.
As a matter of fact, my HP does not give me bad groups either now that I think about it. So I guess I would have to say something has happened with the factory ammo out there now. Or maybe I have just mellowed - or both. So I do not find its accuracy to be inherently different from other comparable carry calibers - at least in present day times anyway.
I recently was shooting a variety of 40 rounds both factory and a limited number of reloads, in testing a newly acquired chronograph. Honestly I was paying more attention to not killing my chorno that I was my target, lol. But I had a farily decent one holer about 10 yds away when I was through. It was not a 1 incher, but again I was paying more attention to my taped areas on my rods than my target. It was probably more like one inch wide and maybe two inches high when I had fired all the various factory and handloads.
I do admit I am a major 357 Sig fan these days. I did notice when I had finished firing 70 rounds of assorted factory and reloads through my chorno with that caliber, my target was more of a 1 incher period. But I have found that round to be amazingly accurate too.
During test firing I was shooting as rapidly as I could. As soon as my buddy told me he had a reading I fired again. But I think the results I obtained would be more than adequate for social purposes or LEO carry purposes. I am not a competitve shooter, and never have been. But I do know from talking with a couple of such shooters, the 40 is being used more and more by a lot of shooters with good results. So I think that too would seem to establish it is certainly accurate enough for most things the average shooter would need to do with it.
That being said, I have to be honest, most of my 40s now live with a 357 Sig barrel in them too. But again, that is really why they make Fords, Chevys and a ton of other brands - so folks can drive what they want. Just my thoughts for what they are worth, others may disagree.