I would like to use an SD card on an Overo as removable storage.  To this end, I have succeeded with the following (ugly kludge of a) procedure:
0. Install a kernel with omap_hsmmc and mmc_block drivers as modules.
1. Insert SD card.
2. Load modules (modprobe omap_hsmmc ; modprobe mmc_block)
3. Mount block device in filesystem (eg. mount /dev/mmcblock0p1 /media/sdhc)
4. Use the card.
5. Unmount the card (eg. umount /media/sdhc)
6. Unload the modules (modprobe -r omap_hsmmc mmc_block)
7. Remove card.
8. Goto step 1.
The problem with the above hack is that removing the omap_hsmmc module disconnects all devices connected to the MMC buses (i.e. SD card and WiFi I think).  Currently, I'm not using WiFi, but I may need it in the near future.
I'd like to know if there is a way to disable just the mmc0 bus instead of all mmc buses.  I've tried messing around with the /sys filesystem, but I haven't found a way to cause the omap_hsmmc module to re-probe the mmc0 bus without removing and inserting the driver.