Dear bombmaniac,
I have had good luck sharing files among many computers using Windows Live Sync (sync.live.com) — it uses peer-sharing, much like Napster and other file sharing programs to instantly distribute a set of files among many computers.
I use it for backing up, too — for instance, when my mother changes a document on her system, it automatically changes the document on my hard drive. This way, despite her unwillingness to backup her documents and photos, I have a complete set of her docs and pics on my computer. When I back up my hard drives, her stuff gets
backed up.
I also use it for clients’ office computers, if they have three office computers and one home computers, I share all the documents and email among the four computers. Then, most of their backing up is automatic, and they need only back up one machine.