I thought I'd share that I have just an what I consider to be exemplary support from Sandisk from whom I bought a 64GB SDXC Card for my S3 about 5 months ago when I was in the US from BUY.COM.
I emailed them at 11:40pm to lodge a troubleshooting ticket as my card won't stay mounted. I enquired if I would have to return the card to the point of purchase (Which when I purchase I understood was likely).
3 Hours later I got a polite and helpful response offering to replace the card, and assuring me they would ship me a forward replacement and no return of the old card was required.
I am very impressed indeed.