Since I'm based there, this Captain usually forgets the noise abatement PA. In the 737-800 it really isn't that noticably different, but in the MD90 it was very noticable (you couldn't going to attempt to stand even if you wanted to).
No, we don't shut off the engines. There is a significantly greater thrust reduction than normal until over the ocean and 3,000 or 4,000 feet altitude.
Yes, it is for noise abatement only. If _anything_ goes wrong (or simply not "perfect"), the noise abatement profile goes out the window and we fly to keep everybody safe --haven't had to do that, but its briefed before every takeoff.