I bought an M&P40 in December of '09 and it is part of my carry stable. Not one of my primary carry guns, that is reserved for one of my 3G Glock 23's, but certainly a gun I would, and have on occasion, carry. It has a great feel to it, is comfortable, does a fine job of handling the .40S&W, and is pretty darned accurate. They do tend to come with rather poor triggers (the action is a SAO (Single Action Only) hybrid), but there is something I found that was simple to correct the trigger on my M&P40.
After carefully examining the internals and how the trigger works in conjunction with the striker safety and the sear, I began a process of working the trigger many times. First, make sure the gun is not loaded. Check this again. Then what I would do was to pull the trigger for one dry fire, then just start pulling the trigger rapidly hundreds of times at a sitting. I have probably done this over 6,000 times to date. The result was a natural smoothing out of the trigger bar, the tang on the bar that rides on the striker safety, and the sear. Of course, I cleaned it before starting this. The trigger now feels much better and more smooth and predictable. It definitely made a difference with my M&P40.
These are good guns and do make a fine carry piece. I am not sorry one bit I bought it. However, my primary G23 still takes first place on my side when I reach for a carry gun.