My serial number is DXX12## and I just purchased it July 14, 2012, and after 100 rounds, the extended magazine is doing the exact same thing as everybody else's here.
Dropping out after the first round is fired.

I called S&W Customer Service, and after 20 minutes on hold, I spoke to a rep who acted like it was the very first time he had heard of this issue, offered absolutely no suggestions or ideas as to what the issue(s) is, and that I needed to send the weapon in to them for service. Period.
When I pressed a little bit, he did finally acknowledge that he had actually heard of the problem, but absolutely nothing else.

This is really disappointing, I was looking forward to getting this weapon, and now I have to send it back and be without it for at least 3 weeks (10 business days quoted for repair + shipping both ways).

When a company is manufacturing weapons designed for personal defense, a lot more quality control should be involved.

In my opinion, Smith & Wesson really dropped the ball on this one.