my brothers and i have been messing around with S beam and group cast, truly awesome.
some of the motion controls like double tap to top of menu, or shake to update email, facebook etc are great.
also the panoramic camera mode is incredible!
one of my brothers has an S2 and he thought it was the same, so we compared it, and the S3 actually has a wider panoramic view and it takes half the time to take it than the S2 does.
another good one i havent messed with is the auto face tagging in pics, i havent messed with it so i dunno how it works, but if you've got it working, just a take a picture of them, and then show them how all you gotta do is tap on their face and get an option to send it to them right away.
and then as well, if you've got the stuff you can blow them away with all the USB, bluetooth and MHL connectivity. the other day i was playing n64 games on the big screen through my phone, wirelessly using a PS3 controller, truly awesome.
you could also blow them away by showing them your battery life, i went over 40 hours without charging and had 68% battery having used 1 hour of screen time.