There are few posts here about the M&P. I have one and after a trip back to S&W, it's turned into a fine shooter that really strated to come into its own after 1,000 to 1,200 rounds.
Problems for me: Gritty trigger. Since mine was gritty, depending on the angle of my trigger finger, I had to apply different amounts of pressure to make the trigger break evenly. I much rather have a smooth trigger with equal resistance and a heavy pull than a gritty one since you can get used to the reset easier. It's not perfect, but its better now.
2nd and most irritating problem was that it extracted brass and dumped it on my head. I tried different ammo to see if that was the problem. Nope. Same 'ol, same 'ol. When I looked into the chamber I could see where the spent cartridges were impacting the inside of the pistol before being fully sent from the gun.
I will say, S&W's customer service was primo. Had the gun returned within three weeks. Stated that they fixed the extractor and tightened the barrel assembly a bit. Gave me a free mag for my trouble and haven't had a problem since. It is a nice shooter and I like it almost as well as my XD that I have had SA work on.
For what it's worth, it is the most comfortable handle on a pistol I have tried with the small backstrap in place. I have small hands and highly recommend the grip on this particular gun for those thinking about grips, all other things being equal.