I agree with the OP. I have the s3 since its release and used an original sandisk 32gb card with no problems. However, yesterday for some reason I started getting error messages that my sd card was unmounted, or unsupported, blank, etc. After googling this problem I see many many people all over the place are having problems with the s3 and sd cards. Google it yourself and see.
I even tried putting the card in the pc to reformat it but it didn't recognize it. So after putting it back in the phone after three hours the s3 decided to recognize the card and so far its not giving me error messages yet. But people the s3 definitely has issues with sd cards and its only a matter of time till you see so yourselves!