The placement of the buttons were fine on my smaller Captivate, but on the larger SGS III, they're really hard for me to get used to. I carry my phone when I run (GPS/Endomondo), and I can't carry it in my right hand. I usually swap hands every so often. When I hold it in my right hand, I keep pressing all the buttons. Seems to work fine in my left.
For me, the volume rocker really gets in the way if I want to set the phone down to take a picture. I try to set it on its side for stability, then the picture starts zooming in and out because I'm putting pressure on the volume rocker.