Richard Hutnik wrote:

Wouldn't it be possible to use this [packet sniffing] ability
to have a cheap way to broadcast sound or video over the Net
to a large number of people, without taxing bandwidth?

A good idea, but it has been already done. It is called
"multicasting". See:

http://www.nwfusion.com/news/tech/2002/0520tech.html
http://www.geckil.com/~harvest/multicasting/

--
znark