Two OS's, one User folder?

[Eisen Feuer]

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 all—thing 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.

 

[Embio]

I've only ever done this between 10.6 and 10.7, 10.7 and 10.8 etc. The only time things have broken a little bit is between 10.8 and 10.9. By 'broken' I mean I needed to fix permissions a couple of times on reboot in 10.9.

If the program is relatively lightweight you can also run 10.6 in VMware/Parallels/Virtual Box

 

[Eisen Feuer]

The main program, Nuke, is the exact opposite of lightweight. It's super picky about GPUs and is the only program that can fill my 32GB of RAM to the brim in less than a minute.

I'm upgrading to 10.8 only because I'm having (documented) system+OS issues that make Adobe Premiere CS6 crash mercilessly, as well as the fact that I'm missing out on a lot of shiny new software that's left the stable perfection of Snow Kitty behind...

 

[Bear]

...
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?
...

The issue you will run in to is where the preferences for something included with OS X are different enough that it causes issues switching back and forth. Apple Mail will be a real issue if you run it under both versions of OS X - there were changes to how it stores mail on your disk. And if you need different versions of a non-Apple application there could be preference issues as well.

It could work fine, but I wouldn't bet on it for something that was where I made my money.

 

[Eisen Feuer]

Thank you that's exactly the answer I was looking for. I know how I'll approach this from here on out