Do Automated Cross-Platform Network Backups The Easy Way, Part 1 - page 2
BackupPC has some limitations on Windows backups. It performs data backups reliably, but it's not suitable for making Windows system restoration images.
BackupPC makes Windows file backups from Samba shares, so it suffers the same limitations as Samba- Windows file ACLs are different from Unix file attributes, and they are more complex and more difficult to understand. So you get the Samba translation instead of the original ACLs. It is not uncommon for them to be set incorrectly, which is not Samba's fault. Under ordinary circumstances this is not a problem. At worst you'll have the nuisance of manually correcting them after restoring from backup.
BackupPC will not backup files that are locked when they are open, such as the Windows Registry, Outlook's
.pst, and database files. Most databases have their own backup utilities which you should use in any case, because backing up a database is a specialized operation. Outlook users should be running the Personal Folder backup utility, then BackupPC can copy the backup file. Because Outlook stores everything in a single monolithic
.pst file, in a fragile, proprietary, binary file format, you want to take extra care to make sure it is being backed up regularly. Or switch to a mail client that is not such a headache.