a few days ago i was looking for some kind of a possibility to tell a user, that he can only copy files from a specified directory. no login, only copying files from this directory. i was looking for some kind of a jail.
i found a really nice howto for a chroot jail to lock users into their home directories. the funny thing is that the user does not know that he is in a jail. it looks like a usual unix environment. you have also the possibility to allow scp, sftp and/or rsync.