Actually, the workaround doesn't work, unless I want to keep getting duplicate files. I have to leave a file there as long as I'm doing searches that might turn it up, or it won't show as something I already have.

I saw someone mention in a thread somewhere using zero length files of the same name. Would that avoid the problem? Hashing a zero length file shouldn't exactly take long. In fact Limewire ought sensibly to ignore such files except for the purposes of generating "file already exists, overwrite?" prompts.

That's the only way to keep track of a lot of files you already have without doing it in ram I think -- that or keeping the actual files themselves in the download directory indefinitely. Without either a duplicate hash or a duplicate file name Limewire will have no way of flagging duplicates in search results, and it seems keeping all the hashes of every file ever downloaded is prohibitively slow and expensive...