I have a 9mm M&P Pro from late 2010 production and it shoots about 8" groups from a bag rest at 25 yds. My Glock and Sigs shoot about 2"-3" from the same rest. I tried different ammo and still had the same results. You can say that maybe its the old saying of its the indian not the arrow but from my internet search and from what i have seen of other more experienced shooters the problem seems to be the gun's barrel.
You can find some other posts here on the forum or also take a look at other forums or trainers websites for info. Some of the sites are below that I found while i was trying to see why my gun shot so bad.
http://10-8performance.blogspot.com/2012/06/s-m-barrels.html
http://mp-pistol.com/smith-wesson-mp-forums.php
http://www.kyledefoor.com/2011/01/answers.html
http://www.apextactical.com/blog/index.php/random-apex/first-shots-with-the-mp-barrel/
http://pistol-forum.com/showthread.php?2903-Recent-manufacture-M-amp-P-9-accuracy
Bottom line from what I have read the issue seems to be the barrel lock up but some also argue that twist rate affects the accuracy with different bullet weights.
As it is right now i have seen picture comparing early production barrels and newer barrels and they have slightly different dimesions.
Ultimately if you like the platform and don't mind having to maybe change out the barrels then go for it. If not try something else. From what I have heard S&W might change out your barrel if you send it in and they deem the accuracy to be sub par. However, I have personally not tried that.