I'm behind a firewall, and I don't get any uploads although I share quite a few files. I think the problem is that Swapper send IP of 0.0.0.0 for firewalled hosts, that other clients simply ignore. A possible solution is to implement the get IP from peers mechanism (as in Gnucleus 1.6.3.0) and give the real IP address, even if ut is not really useful to the peers because of the firewall.