I've been courting the ability to have my OS installed separately on an SSD with the big stuff (My Users folder) aliased and stored on a HDD. I'm simultaneously, and VERY tentatively, looking to install Mountain Lion over my long-time Snow Leopard install; my immediate fear being some of my money-making applications will break compatibility upon upgrading. I'm wondering, to those with a little more advanced knowledge of OS X's inner workings, would it be possible to have a 10.6 and 10.8 install on different Hard Drives, with a shared Users folder stored elsewhere for both? When I was tinkering around with the SSD scenario I found it's possible to boot into OS X with no Users folder at allthing is, can something be changed by 10.8 in the users folder that would make it corrupt/invisible/unusable by 10.6, or vice versa? For example, the Applications folder is tied to the system with supporting data in /Library/Application Support and /Library/Preferences. These things would change as I messed with the apps I presume, meanwhile I would have unchanging data in home/Library.