(Get ready for a long read... Sorry)
Keep this in mind when researching any gun on the various Forums...
- Most people find a forum, only AFTER they have a problem, so many/most threads are going to be 'problem'/'issue' threads. 95% (if not 99%) of Shield owners are more than happy with their Shield.
- When many have a problem/issue/failure, they want EVERYONE to know about it, so they post Duplicate threads on multiple Forums. 10 people posting their 1 problem, on 10 forums, make it look like 100 instances of the problem.
- Many other people, reply to a problem, saying "I've seen LOTS of people posting about this issue on other forums", not realizing that it's the same single instance.
Basically the old "You tell 2 friends and they'll tell 2 friends, and over and over and over" scenario... Making a handful of true issues, SEEM like an epidemic. 
One of the kings of Shield issues is the Recoil Spring Assembly. A few have been reported as the rear disk being bent.
Could it have happened due to improper seating during assembly? Possibly.
Could it have been bent before leaving the Factory? Possibly.
Has it been such an issue (in these first 3 yrs), that S&W has seen fit to modify it? Nope. If it were, they would have modified it.
How can you be relatively certain that YOU get a good Shield?
Before putting your money/card on the counter and filling out the Form 4473, have the sales person Field Strip it, so you can inspect the rails, feed ramp, lug (any problem spots you've read about) and ensure that the RSA's rear disk is unbent. If it doesn't pass your inspection, point out any discrepancies and request them to bring out another. Doing this will also act as a walk through on Field Stripping and assembly. I do this with EVERY pistol purchase now-a-days.
Also... If you're also considering the G43 and XD-S (may as well add the LC9S/LC9S Pro to the mix), try to shoot each of these contenders before buying. (Don't rely on how nice they feel to fondle at the counter)
I've had my Shield for over 3yrs now and it's been flawless. It DID have a Super Tight RSA, making it difficult to rack at first and I did need to ensure that the RSA was properly aligned on its shelf during assembly. While the XD-S, G43 and LC9 ALL feel nice in the hand, to me, the Shield feels much nicer to shoot than the XD-S and LC9. I have not yet had a chance to shoot the G43.