A tool that collects info about the clients that share would be cool! I'm using BearShare, and there you can log those who download from you.
Out of the 3584 Distinct IPs that've downloaded from me the last three weeks,
45% had BearShare
41% had LimeWire
6% had Gnotella
4% had Gnucleus
3% had MyNapster

I'm sorry to say, but I would've voted in favour of BearShare.