In 2007, i got my first DSLR, a K10, and outfitted it with the Tamron 18-250. The first thing i bumped into was fuzzy pictures.
Being a faithful reader of pentax forums, i immediately jumped to the conclusion that my fuzzy pictures were a faulty lens. Just to be sure, i slapped it on a tripod and my pictures came out sharp. Ah-ha moment, it wasn't the lens, but the way i was using it. I started using appropriate shutter speeds and the OOFs went away, mostly.
Now jump ahead 4 1/2 years, and someone posts this fascinating discussion of the problems with Nikon's VR system. His advice, if i remember it right, was to generally not use VR unless one is in those specific few situations where it works.
Nikon VR explained
Now jump to the immediately preceding post by me which quotes Gimbal. If you keep your finger on the half press, one would think with the lit hand icon that SR is fully functioning. If you lift your finger on the half press, with the SR system still engage, you find it fading in an out for 2 seconds at a time at every small movement of the camera (except for tiny movements)
The tolerances to maintain a phase focusing system are definitely problematic, but i believe that SR and VR systems are equally problematic for the majority of camera users and are also contributing to OOF shots in all camera brands.
There is a simple way to prevent SR responsible OOF shots. DO NOT USE SR IN PANNING, ACTION MOVEMENT, SIDEWALK SHOOTING, UNLESS ONE UNDERSTANDS THE SR/VR RISK.
I'm not unhappy with my K5 and previous Pentax dslrs. I get really high acceptance rates, like perhaps 95% in focus) for indoor play rehearsal shots shooting when i get all my parameters set correctly. (one of my useful settings was to disable SR) Of course every once in a while, they choose a play with very moody lighting and i struggle, but thats a general limitation iwth all brands. How do i know that? Because i often shoot theatre with photogs who have Canon, Nikon cameras such as the 60D, the D300, D300s, D7000. (We step into the lobby during the break and all complain about the inadequate lighting - misery loves company :-))
Perhaps i'm exaggerating a small bit, but its to get folks attention. There is definitely a problem out there with these systems like SR and VR.