One of the first things I did when I got my BlackBerry Z10 was plug in a 64GB MicroSDXC card to see if it would work. Sadly it did not work immediately with the exFAT format that it is formatted with by default but RIM is adding exFAT support after launch. The trick to get it to work is to simply format the SD card using the options and you will get FAT32 partition that works like a charm and sees the whole 64GB.
I am absolutely loving the ability to blow past the 32GB limit of previous MicroSDHC cards. Microsoft owns both of the main standards for larger file systems namely NTFS and exFAT and RIM has already confirmed that they have licensed the technology so expect it to come after launch.
Personally I find MicroSDXC support promising since it means users will be able to add 64GB+ cards at launch and up to 2 terabyte cards in the future. You can pick up a 64GB MicroSDXC cards on Amazon for less than $60 shipped now and prices will only continue to go down as larger sizes come out. In other words we will be packing some serious storage into your BlackBerrys in the future!
PS: Anyone else think its crazy that they can pack in 64GB into something smaller than your fingernail?