For user files only (ie, My Documents or whatever) can you set up network based home directories ? And then just back up the server they live on.
If you do this, you better have an insanely reliable network with at least gigabit speeds. Where I work we have all of our *nix boxes set up with the user home directories on NFS and when the network goes out, we have a lot of employees who can't do their jobs. Even a few hours of outage can be extremely costly. On top of that, no one who works with large files uses their home directory for anything due to the limited space and slow (100Mbps) network speeds. Instead everything is stored locally and backups are up to the end user (read "non-existent").