Got myself one of these the other week, thought I'd better stick to a 'brand' so got a Sandisk. its HDXC - which I checked should work with my Galaxy S3..
Arrived in the post - stuck it in my phone happy days.
Took a load of photos at the weekend and behold, half of them a unreadable, corrupted or what ever. Bit gutted obviously.
Seems you have to format the card using your phone before use. Nobody tells you that do they!!
Which I've done (overwriting all the corrupt photos) and everything seems hundy dory now... so just a word to the wise - format your new microSD card prior to use!!!