I got a Samsung Galaxy SIII, and when I first got it, I feel like it auto-corrected my typing. When I was busy exploring my phone and setting it up the way I wanted it, I think I messed with some setting that I shouldn't have, and a few features on my phone were being screwy.
So, being the genius that I am <sarcasm font>, I chose to "factory reset" my phone. But now I feel like the auto-correct doesn't work. I've tried to mess with the keyboard settings, but I can't seem to get it to automatically correct my typing.
My suggestion, use this keyboard instead of the stock one...the auto correct is ON POINT and is much better than the stock keyboard...you can also add themes to it, and its FREE! They have a paid version but its definitely worth buying, but try the free one