I have the S3 and I use mine mainly for shooting telemark festivals so it is on snow a lot. I'd recommend getting an adapter tube and UV and/or polarizing filter from
Lensmate. It adds protection for the lens and needed polarizing filter for bright light shots on snow.
Taking stills while shooting video will cause a noticeable pause in the video. It's not bad, but definitely not seamless.
I have a case that I clip to my camelback pack and run through the hip belt so it's secured in two places.
-dave-