Exciting news for stingy mac nerds.  Well, realistically kinda mac nerds, because a true mac nerd would either know about this already, or would not care because they don’t need time machine.  I have a headless Macintosh running in my home, with an array of external hard drives connected to it and served using AFP.  I originally had an old Windows XP machine running as a Samba share to my mac to host my movies.  That said, AFP and OS X are far nicer to work with.  Anyhow with one simple copy/paste command line cue one can use a shared volume to automatically backup their computer every time said computer connects to said network, and all without a single wire.  That command that needs to be entered is:

defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

(to undo the command one would enter the same command with zero in place of 1)

From there you simply use the Time Machine interface to setup your backup.

Fantastico!