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sudo dpkg-reconfigure adduser

That will pop up a dialog which will ask you whether you want
system-wide readable home directories. If you select no, then new home
directories would not be readable by other users by default.

You can do a "sudo chmod 700 ~" as the admin user which would deny
access by other users to the admin directory.

I guess you could run nautilus as root to browse the other users' data,
but that could be a bit dangerous in itself, so I hope there's some
better suggestions for that part out there.

-Jonathan