You want to know why ?
Because it has no central point .
They can't bring the network down , no matter wich lawsuits they get against them .
Now Napster was easy to shut down .
There was one central server , you just hit the switch and it was over .

Witch Gnutella you can't ; it's not technically possible .
The hostcaches you say , but everyone can start one .
And I admit the Gnutella network has some problems with scaling but there working on that .

Lemme tell you something : the FastTrack network has the same problem as Napster .
If the damn lawyers decide to turn of the switch at the central servers it's over .

You rate the clients by the number of results you get but did you look at the internals and the technical differences of those networks ?

I prefer to go with an network that will still exist tomorow .
Even if it has some more problems then others .