Despite the popular misconception that the difference between SDHC and SDXC is absolute, many people are using these SDXC cards in SDHC devices with no troubles. I have a Kingmax 64gb card on the way, so we should know next week. It's reported to work on the Bionic, so even if it doesn't work on the Nook i still have a use for it. Perhaps people still recall the sd to sdhc incompatibilities, but doesn't seem to be the same with sdhc to sdxc.
Sandisk 64GB Micro SDXC Vs Samsung Galaxy S II - YouTube
Secure Digital - Wikipedia, the free encyclopedia
"SDHC and SDXC compatibility issues
In the 3.0 specification, the electronic interface of SDHC and SDXC cards is the same. This means that SDHC hosts that have drivers that recognize the newly used capability bits, and have operating system software that understands the exFAT filesystem, are compatible with SDXC cards. The decision to label cards with a capacity greater than 32 GB as SDXC and to use a different filesystem is due solely to the limitations in creating larger filesystems in certain versions of Microsoft Windows.[citation needed] Other operating system kernels, such as Linux, make no distinction between SDHC and SDXC cards, as long as the card contains a compatible filesystem.
SDHC and SDXC cards and hosts have these compatibility issues:
Existing SDHC hosts will only support the SDXC cards at up to UHS104 speeds.[45]
SDXC hosts are backward compatible with SD and SDHC memory cards.[62]
The operating systems that support SDXC, as of 2011, are: Linux (with a proprietary driver for the exFAT filesystem),[63] Microsoft Windows 7, Windows Vista SP1+,[62] Windows XP SP2 or SP3 with KB955704,[64] Windows Server 2008 SP1+, Windows Server 2003 SP2 or SP3 with KB955704, Windows CE 6+, Mac OS X 10.6.5 or later.[65]"