backup question

[U233A at wvnvm.wvnet.edu]

     What ramifications are there in backing up the system
while users are still logged on?  In addition, we do not
unmount the filesystems prior to the backup executing.
It appears that under both of those circumstances, the filesystems
are being backed up ok.  I havn't had any problems so far in
restoring files that were backed up under these conditions.

I'd be glad for advice.  Thanks---/tony