Those types of files are obviously not being churned out onto the network by your average user. However they may accidentally downld them & keep them is their share folder until they've checked them.

If you have LW 4.10 then learn to filter out the junk. A quick description of what to filter out (click on link) As for dud mp3's, I guess it depends. Some mp3's from other gnutella clients don't necessarily show the bit rate until after you've downlded them. But then yes there's also those that don't show bit rate & are basically unplayable. I found I had some issues with ogg files but they're different.