This is not as simple a subject as it might seem, and it is for instance difficult if not impossible(I forget which) to browse Bearshare from Limewire. Firewall set ups, router use by hosts, and the fact that they may download on one machine and share from another, are the sort of things that make it virtually impossible to see who is not sharing (or "freeloading") and who is.
Browsing hosts is not a perfect science
If you use the search button above right and look for freeloader you will find many threads on the subject.
Certainly there are a lot of freeloaders out there, and the only way you can really tell who they are is by intuition, and even that will probably not be much use.
I hope this sort of answers your question. There is a freelader filter in Limewire, but opinions vary as to whether it works atall