I own a MP9 and I highly recommend it. It is on par with my XDs or Glocks, but with much better ergos.
There were some issues with mags dropping, strikers breaking, and rusting when they first came out but it appears those issues have all been corrected. If you do have a problem, you can count of S&W to take care of you. Their customer service is excellent.
Before anyone mentions anything too negative about the early problems, I would caution them to remember that even the Glocks had issues in the first gen......as much as they try to forget.