This explains it all from the
http://eff.org site ->
http://tor.eff.org/index.html.en"> The Tor "Onion Router" Project
Please consider donating some bandwidth... Try first as a client, I did and it was a little slow, but being able to turn it on-off via the Firefox "TorButton" makes it easy to jump on/off the network as desired. I like what I see - so now I'm helping others by participating as a server node.
Here is an excerpt from the EFF page with the pitch....
The Tor network relies on volunteers to donate bandwidth. The more people who run servers, the faster the Tor network will be. If you have at least 20 kilobytes/s each way, please help out Tor by configuring your Tor to be a server too. We have many features that make Tor servers easy and convenient, including rate limiting for bandwidth, exit policies so you can limit your exposure to abuse complaints, and support for dynamic IP addresses.
Peace,
MZr7