I bought one of the first ones out last April and have had ZERO problems. It's had the living daylights shot out of it from me shooting it and letting other people see how they liked it. It's had about everything shot through it.
I ordered one from my LGS as soon as I found out about them right around the Shot Show time last year. It was a no brainer that it was going to be one hot handgun at that size.
I hear you. the reason I ordered two was because how well my brother's shot, the mrs. liked it, so I ordered up two of them. His Bodyguard, on the other hand, is probably due for a second return to S&W. But it's well documented that the following have occured with the Shield and S&W has formally, at least to the customers, addressed most of these issues:
1 - magazines dropping during the course of fire. S&W is replacing magazine catches.
2 - The drift pin, forward of the trigger, has been known to walk out. S&W states that the vendor went off spec, and they are replacing the pins for customers.
3 - Damaged rear of a slide, from normal operation, posted on this forum. I can't imagine ammo, etc., could have caused that. It seems to be making contact where it shouldn't.
4 - The worst was just posted. A 40 S&W Shield that most likely had hot, reloaded, Glaser rounds put in it. While I agree these aren't made for hot loads, the darn gun blew up in his hand. Honestly, I will never buy a 40 S&W caliber polymer gun. I know thousands are working out just fine, but the 40 seems too hot for polymer, Glock was the first to experience that. plus, I don't like the way a polymer-framed handles the recoil of a 40. The M&P full size is probably the most comfortable 40 I've shot, but most compacts, like the G23, just aren't fun for me to shoot.