The M&P is a great handgun, but on many of them I have heard the triggers are kind of ugly for a while. It is not a real clean, crisp break at first, but I noticed a marked improvement in mine after the first 100 rounds or so. I have heard that after 250 or so it has polished itself up a bit and is pretty nice.
Indeed, the only complaint I have about my MP40 is the trigger (but it is not too bad now after 200 rounds and improving). I have been able to get pretty decent groups out of some cheap (relatively) Blazer Brass rounds as well as the WWB that I have been using to break in the gun a little. After about 500 rounds or so, I will start checking for accuracy loads with it.
When all is said and done, I believe the M&P is one of the finest polymers out there on the market today. It was a tough choice between it and the XDm but have never regretted the decision to go with the "made in USA".