Check the links above [in robriccs post].

Basically Turbonet is faster and cheaper than tivonet.
For SA tivos it lets you extract the video from a Tivo and either share it with your
friends via VCD or possibly DVD or even just as a large AVi or whatever files.

Also if you install the Tivoweb software for the Tivo you can have a nifty web interface to any tivo for managing your programming/now showing and you can even change the data for each recorded show or edit season passses or even schedule new shows.

If neither of these lights your candle then you don't need it.