I found this SDHC driver for the Sharp ROM on a blog called "Puchi no izu":
http://petit-noise.net/download/sdhc-driverThe author (bucchi) says that he has experienced good stability but, as always, try at your own risk. The driver supports up to 32 GB. I installed it on my SL-C750 with Sharp ROM.
Mounted and accessed files, no problems:
2 GB SanDisk (Class 2)
8 GB SanDisk Ultra 2 (Class 4)
I didn't do any speed tests or any writing.
I also tried an 8 GB SanDisk Ultra (Class 4) - would not mount, but dmesg showed the partitions were found. The automounter only looks for VFAT I guess and the VFAT partition is one of the extended partitions. All the others are ext2. I will look into mounting this one manually.
This driver is much better packaged than the C-guys one.
If you try it, please reply to this thread with your results. Thanks.