There is a setting for the number of files a person has to share before they can connect to you (tools->Options->Advanced->Preferencing). I leave my setting at the default (freeloaders can connect), but heard that sharing more than 100 files increased your chances at better connections. I rarely hear of anyone who changes that setting, but who knows? Some people really dislike leeches and would set that number higher.

Anyway, I prefer to see as much or more uploads as downloads. Anyone can be a leech and fair is fair.