Of course each oft the systems have to have their own passwd file, wtf.. unless you're authenticating to ldap or another service.
The solution is to have the folder you are mounting to in fstab, and tell it to always mount media as a specific UID/Group
Also, the "display or execute" message isn't a problem with the OS, it's a file manager issue. I'm guessing if it annoys you that much, then somebody would have by now submitted it as a bug/idea, and the project admins could decide whether to make it not display that message & just do what's right, or to put an option in somewhere to disable the message. It shouldn't have to ask since it can look up the file extension and then pass it through the binary wrappers