I cannot speak much on it. I held one and almost considered buying it in place of my much more concealable S&W Bodyguard. I wanted one pretty bad despite it not fitting my needs but the guy told me they are on special order and their is a waiting list. Holding it you can tell it is a pretty remarkable gun. The trigger is updated (M&P triggers were pretty good before, but this is supposed to be even better). The size is crazy, it feels so good in your hands! If you have the $$$ which btw they are pretty cheap, I would highly recommend. I want one pretty bad too!
On a negative note, the cops in my area are changing out their Glocks for M&Ps (not shields that I know of). When I give my cop buddies shit on their new guns they get alittle disgruntled. They claim that the M&Ps rust pretty bad. I can't say this out of my own experiences, but knowing S&W they are a good company so even if this is true, they backup their guns for life. Something to research if you get the chance. The M&P Shield probably doesn't have this problem though.
The price point and concealability of the M&P Shield makes it a great choice. Good luck finding one!