According to a kbase note just published by Apple:
Can I install Mac OS X on an SD storage device and use it as a startup volume?Yes. Change the default partition table to GUID using Disk Utility, and format the card to use the Mac OS Extended file format to do so.
Wow, that might come in handy as an emergency backup solution takes less space than a disc. Or simply clone your OSX install DVD onto an SDHC card and carry it around.
