I don't have the .40 I have a sub-compact 9mm and I think it is a awesome firearm! It breaks down easily, easy to clean, and shots perfectly straight.
Good luck on finding a .40 version, it took me awhile to get the 9mm at a good price so make sure if you have to get it from a shop that you shop around first, and budsgunshop.com looks like they have some in stock but you need to email them for a price - Beretta PX4 D .40S&W 2-14RD SHIPS FREE
I had one in 9mm and it was a great gun. VERY accurate! It shot and functioned flawlessly. If the 40 is the same as the 9, which I assume it will be, you will not be disappointed!
I have the full size 9mm and I love it. Easy to clean and field strip, shoots as straight as I can shoot it, and the rotating barrel recoil system is nice as well. Since it is not as common as other pistols out there, I get lots of questions and it is fun to show off a bit. The negative is the expensive accessories - only OEM mags are available at around 30-40 a piece, etc.