To facilitate getting stuff to my Transformer Prime, I picked up a 32GB microSD card.
It's great that the Prime has a microSD card slot, but there's a rather significant flaw with it that people have found and discussed on on various forums. Because the sides of the Prime tapers off toward the back, rather than being flat, a chunk of the SD card sticks out. The card holder uses the traditional push spring retention mechanism (push to lock it in, push to pop it out). It's actually pretty easy to accidentally pop the SD card out.
I think if Asus had recessed the SD card holder a couple more millimeters in so that the card is flush with the back part of the slot instead of the top part of the slot, problems with accidental ejection would be eliminated.