The software should allow you to write a script to tell it what files to backup and when. In addition to allowing you to run backup unattended, the software should let you back up the server from any workstation. This way, the network administrator can perform backups from his or her desk, and the server can be safely locked away in the closet or computer room. The software should allow local workstations to be backed up. Users won't remember to back up their local hard disks regularly.
Security is a major issue.
You don't want someone with a tape drive to walk off with the contents of the server disk. The software should require a password. Some products require that the software log in as the supervisor, which is bad, because the person performing the backup should not necessarily have access to every bit of information on the network. If you do it right, backup will ensure that you will lose only a day's work. But even a day's lost work can be too much.