I've seen references about having a dedicated User directory that is shared between OS's. Right now I have a SL drive, a ML drive, and will be adding Mavericks. (I still need the other two OS's). The bulk of my user data is on my ML drive and symbolic linked to SL. This works well, however there were a couple instances/different app needs where I did have to copy the original folder and put it on SL because I soon noticed the app wasn't properly writing to or reading from the original on ML with the symbolic link (or alias either), and it needed the real thing to do its job right.

However this could also have been because I never had gone into the account settings and officially set ML as the new User directory location. Does doing so that fix most issues such as this?

Another scenario is that some folders may still need to be present on each OS because it is using a different version of the app due to the OS requirement?

If possible though I would like to still share the data since I do use the same app depending on whatever OS I happen to be in. And of course for things like accounting apps/checkbooks and other apps with presets, etc. As I mentioned, this works really well for me currently except for those couple instances.