So do you know for a fact that the presence of slow upload users doesn't degrade the performance of the network, or are you just guessing? Say there are 100 possible sources in a search, how does the Limewire client pick amongst them? Is it going to routinely pass on sources that can give a continuous upload stream for crappy upload rates from people in my situation?

The safe thing is obviously to just share everything, but I'm interested in the optimal decision. I don't know enough about the program's internal workings to make a judgement.