Personally.. after owning a few and reading and shooting a lot.. I sold all my .40cals.
Main reasons... I prefer the 1911 platform. So clearly I stick to .45acp a lot. I am comfortable with it, both in my ability to shoot it, and its performance.
Second reason.. when I am not carrying a 1911, or my XDS for that matter...it is because I want something with more capacity... so I will go to a 9mm.
Yes a .40cal is the same size as a 9mm, but you are sacrificing a few rounds.. and for what exactly? YES in theory... the .40 is MARGINALLY better, but to be honest.. I don't think its enough of a difference to sacrifice the extra rounds.
I am sure people will be in an uproar and posting gel tests and what not and crunching numbers, and I completely agree, however I would place my bet on 3 more rounds placed center mass over 1mm more diameter, and some extra weight and velocity. If you read some autopsy reports.... generally most hand gun wounds look the same across the board, and caliber isn't determined until the slug is removed.
Not to mention 9mm is still cheaper to shoot, enjoy, and practice with.
Not knocking the .40..... just stating why I personally felt I no longer needed to own any.
Also police forces are starting to release the same thing, and switching back to 9mm's such as my local one did.
I have been mulling over the fact to buy another .40.. but in a 2011 STI for IPSC competition to be in major scoring.