Used a Samsung 32 GB Micro Sd Class 10 in an adapter. Put it into my Win 7 64 bit PC and dragged about 10 GB of music onto it. Took about 10 minutes. Getting ready for my Verizon 32 GB Pebble Blue.
Class speed of the card determines how fast files will transfer on to the card (write speed). i.e. Class 10 is faster than Class 4 generally speaking. Different brands of cards vary in speed.