I don't share my downloads file folder for 2 very specific reasons.
I test the files before I share them.

1. If they're archive files or possibly virus containing files, I scan them first after they are downloaded and in some cases open them and see if they are corrupted or not in which case would be a shame to share a corrupt or virus infected file would it not? And I have downloaded files that weren't of the typical virus containing zips and rars.

2. I download porn, shamelessly, though sometimes the content is comepletely different than what the filename suggests. It rarely ever happens but some discusting things shouldn't be shared (or be in existance for that matter) in which case I promptly delete it off my hard drive as I will NOT make THAT available to the network.

After these files are tested/viewed/scanned I move them into seperate folders which I do share and refresh my library thus sharing legit and in some cases correctly renamed files.

As far as the leaching problem goes, only the Limewire program itself will know for sure if someone is sharing or not. So perhaps limewire can prevent users who are not sharing by preventing them from searching or downloading till they share. Or a nice lil popup window every 5 minutes that reminds them they aren't sharing anything. Like that smiley central advert that says "SAY SOMETHING"! should be, "SHARE SOMETHING"!! But you get the idea.

Though I suppose someone could share their 115kb emoticon collection and show they're sharing 95 files! woohooooooo! I see no reason why anyone can't share 10mb. That should be the minimum and I'm being generous. I had dialup too for years and I still shared a few hundred files, over 100mb.

It is a file sharing program, not a file leaching program. And those who leach should really not use the program.