I get generic limewire files when the name of the original file is too long - the extension gets lopped off when it gets crammed into 32 characters - but not always, so this is only part of the answer. Maybe some file types are more sensitive to being transferred?

If the type/creator tag gets wiped out during transfers, the file adopts Limewire as its "parent" app by default - that's why they show up as generic limewire docs. To repair the files, you have to re-specify that tag so the right apps can recognize them.

You can try just renaming the clipped file name with the original extension - that sometimes works. Otherwise, get a simple multi-utility like More File Info - http://www.pixture.com/mac-mfi.html - or the more specific FileTyper - http://www.ugcs.caltech.edu/~dazuma/filetyper/ (Both $10 shareware - MFI is not disabled before purchase, don't know about FT)

Either of these apps will let you change the type and creator of a file back to something usable. Say, for an incoming html document that's lost its identity, you could change it from ????/OGx (which id's it as a generic limewire document) to text/MSIE - a text file made by Microsoft Explorer, which any browser will recognize as html.

If all this looks a bit daunting, you might want to go for FileTyper since it's the more specialized and thus more idiot-proof of the 2.

Hope this helps.