I have the Sandisk Ultra SDXC 64 GB card, and once reformatted it works fine in my n800, I formatted it fat32 and the whole 64 GB shows up in n800.

The only issue I had was on my desktop, with the first usb SD card reader from Adata(which I used because it was out), this reader wouldn't see the card as anything other than 32 GB in gparted or windows. I then used my older Sabrent reader which worked fine. Not sure what was up with the adata reader.