A few days ago, I was checking a friend's system for backing up.
It was based on rsync on the linux side and rsync server on a windows machine he uses for storing information generated by other software.
Rsync worked pretty well for him until he started to put several strange characters in filenames which rendered the backup unusable to certain point.
After being asked for alternative backup software that was available on several platforms, I've ended testing duplicity.
As a command line interface tool, it can run pretty well on cron jobs, and eases the management of doing full or incremental backups to several kinds of targets.
Duplicity can also take care of tiding backup store removing older backups and automatically perform a full backup if older than x time, so you can automate the full backup management.
Best of all is the backend support, as you can do backups over rsync, scp, ftp, file, imap, ssh, amazon, webdav, etc , so you can use that old NAS to store your backups without any special support except pretty standard protocols even on low-end models.