I am not trying to defend these people but, many of them are doing this unknowingly I think. Instead of sharing folders with the good stuff in them, they share far too many and, like you, they have downloaded rubbish - where they go wrong is they forget to delete them (possibly they want to keep them as that's the only one they could get) . Do a browse on them and I think you will find many are sharing all sorts of stupid things off their PC - I men, who wants to download cookies and icons from their programs??????
Please SORT OUT YOUR FOLDERS, make sure that what you are sharing is of a good quality (shove them in another folder if they are not - and not a sub folder, Limewire has access to them if they are in a shared folder.
Dump the faulty stuff and share stuff people want.
Of course, don't forget those that want to stop p2p - they have loads of dud files (deliberate) available just to gunge up the works.