The depressing news is here: SDXC
Somehow Microsoft managed to con/bribe/blackmail the Secure Digital committee into making their proprietary exFAT filesystem a mandatory feature of SDXC. Further, evidently some SDXC host controllers expect to find an exFAT formatted filesystem on cards larger than 32GB, and can barf if the user formatted it as something reasonable (like ext4, for example).
Linux support for exFAT is only experimental at this stage. Key components of exFAT are protected behind (frivolous) patents, and Microsoft has refused to publicly release an exFAT specification. As such, all exFAT support under Linux is based on reverse-engineering.
If interoperability isn't a concern (that is, if it isn't necessary for a Windows or Mac system to be able to read your SDXC cards), then you may be able to wipe and reformat the card as ext4, provided the host controller doesn't sabotage you.
There are some reports of people having success re-formatting an SDXC card with plain-jane FAT32.
