Still it looks like the best format if you want to move data between OS X, Win and Linux....
It's for (slow) flash meda. It has a single FAT, instead of two like FAT12, FAT16, FAT32. And it's not journaled. So if you need exFAT ostensibly for a large file system with many files, you're still better off with NTFS and using NTFS-3G from MacPorts to get it on a Mac. It's included in most Linux distros. If you have individual files larger than 4GB, and it's a large file system (but not many files, just large ones) then exFAT is OK but still not as good an option as NTFS.
I'm glad there's an open source option. But to see this format proliferate would be unfortunate. It brings nothing to the table that can't be done with NTFS. UDF would have been a better option for vendors to go with. But not even Apple offers formatting USB sticks or hard drives as UDF. So even though technologically and licensing wise it's superior, for some reason market forces chose the b.s. inferior, IP and royalty encumbered option yet again.
here https://github.com/rxrz/exfat-nofuse is the non-fuse read/write kernel module, works on linux kernel v 3.8.11, does need a fix for 3.9.x but will probably be ported to kernel 4.x as a patch with the start of the new mainline
feel free to fork and/or use in any way