I believe that a majority of Gnutella servants are left on for days, even weeks at a time. Notice how many T1, T3, and DSL connections are present? Most people cannot afford T1 or T3 lines. So where do they come from? From the workplace, and not the home. I'm guessing most people leave LW (or whatever servant/client they have) on at work until they have to restart the computer, which on many NT sytstems, could easily be longer than a week (that is, if it doesn't crash before then). So, theoretically, many of the Gnutella clients could be left on for days at a time (this makes the network much healthier). Also, you may be wondering why you would keep getting pings when no one is searching with their unattended node. But remember, LimeWire is constantly trying to make new connections as others die out or fail.

If you want to clear your host cache, simply go to the connections tab and hit the "clear" button in the bottom-right-hand corner.

Sending pings and pongs (pongs being slightly larger) doesn't consume a whole lot of bandwidth, unless you are sending/receiving massive amounts of them. If you monitor your bandwidth, you will see that the Gnutella traffic can easily clog your connection (dial up is maxed out at somewhere over 2k hosts). Watch your bandwidth when you are connected to thousands of users. Set a limit on how many connections can be maintained at once to limit traffic if need be.

Hope this way-too-long post helped. :-)