Gamer, where did you get those numbers from? I hope you don't rely on that almost 2 year-old paper "Freeride on Gnutella" (or whatever it's called). It's one of the few papers on that topic I've ever found and the numbers aren't true anymore.

You can easily modify an open source client to collect up-to-date data from PONGs.

I did that and no matter what configuration I used (connecting to limewire hosts, morpheus hosts or any other clients), never, more than 25% of the PONGs came from hosts not sharing any files. QueryReplies indicated that less than 15% of all clients sharing files, never had a successful upload. That means at least 64% of all clients are actively sharing files. My (more optimistic) guess is that it's more like 70% to 75%.