To share your files seamlessly across your Linux installations. create your users in such a way that they have the same UID on each distribution -- each with their own dedicated group. For instance. you could have the uid:gid series of 500:500.501:501, and so on. This is the simplest scheme and should work well for a typical home-computing environment. You can also create users in such a way that certain users have access to certain distros and no access to others. You can thus restrict each user to just one distribution if you wish.