Mine suffered a broken hammer pin after a couple of years, and S&W replaced it. That being said...realize that on these boards people usually post when something is unsatisfactory with the gun, and are less likely to post when all is well. And people become more persnickety when they pay top dollar for a pro model. So in addition to the major problems like mine had, you'll see posts like "my 640 Pro shoot left 0.5 inches at 15 yards" and such.

In other words, if I had to do it all over again, I'd still buy the 640 Pro. Its a great little carry gun and I'm very happy with it.