For some time I've been downloading stuff using Bittorrent. The amount of used disk is increasing so fast, the 'backup to desktop' is giving problems. I've changed some things to make sure that some ibays are not backed up anymore. I've been snooping around, and played with Backup to Workstation. There's even a commercial version available.
Of course, no backup means lost data when the disk crashes.
Look here for a full explanation.