I recently started using UbuntuOne, a straightforward folder replication service for Ubuntu GNU/Linux clients. SImple enough that I've moved my main desktop machine to Ubuntu from a different distro to simply backup working files and to have files easily accessible between my main desktop and laptop.
My last remaining MS Windows box has a free Mozy.com account for backing up data files.
Both Mozy and UbuntuOne update automatically as files within their scope are created or updated.
Linux off-site data backups are done via rsync to a rsync.net server.
Bulk backups are done to a couple of 1TB USB external drives, overwritten when new backups are done. DVDs are used for historical snapshots, mainly of binary-format files as most important text-based files are version controlled anyway.