Incremental backups always seemed expensive and time consuming to me, then along came rsnapshot. Basically, the idea is that incremental backups use hard links whenever possible, thereby using a fraction of the disk space full incremental backups would require (and offering faster backup speed as well, I’d reckon). Dirvish sets forth similar promises as rdesktop.
All this hard linking sounds very similar to the way subversion does branching. In some cases, it might be reasonable to use a subversion-backed filesystem, where every write is a commit/checkin. It should be configurable, so certain files could be excluded. It should allow lazy writes.