I have an M&P9c and have had nothing but great success with it. It currently has ~4000 rounds through it without even as much as a hiccup. Overall, I think my M&P9c is an excellent platform for concealed carry. It feels great, points naturally, and conceals easily on my small build. Some M&Pc's have had problems like dropping mags, but these were mostly limited to the M&P40c. I beleive Smith & Wesson has worked this out but if you would get an M&P40c and have issues, they will undoubtedly take care of you.
Also, if you do get an M&P40c, you may want to look into getting some fullsize .40 magazines and ordering a few mag sleeves. Here is a thread I started a while ago about the mag sleeves:M&P Mag Sleeves (picture intensive). Rick (luvmy40) now has a website: Custom Carry Concepts.
As mentioned in an early post, definitely check out MP-Pistol Forum.