When LW user Joe shares a popular file, tons of uploaders will flood his upload slots. This is not desireable for Joe because he is on a DSL connection and he gets penalized whenever he uploads too much.

It's also bad to the network for several reasons:

1) When Joe's upload slots are maxed out, each downloader's download speed will go down.

2) People who want to access Joe's less popular files won't have a chance because Joe's queued up with requests for the more popular file. In general, this translates to less accessible files on the network.

3) A possible result might be that Joe will be more reluctant to share files that are high in demand. (= less files on the network.)

If LW did torrent-styled uploading of popular files, then I envision uploading would work something like this:

User1 asks for Joe's popular file. Joe's LW allows the upload to begin because User1 is the first person to ask. Then comes along User2, asking for the same file. Joe's LW sez: "Gee, sorry, my hands are tied. go ask User1 for a partial download." Then User2's LW sez: "OK! I'll go download from User1." If User1 isn't cooperative with uploading Joe can cut down his download rate and divert traffic to a more cooperative user.

Well, more on better uploading can be gleaned from <a href="http://bitconjurer.org/BitTorrent/">bittorent's</a> website, I suppose.

LW already does torrent-style uploading. It's called Partial File Sharing (PFS)

I thought partial file sharing is good for downloading from multiple sites? What I'm thinking of is for the opposite scenario, where there's one source and many destinations (unless I'm missing something here...)

Nope. Partial File Sharing is not BitTorrent.
I looked up what partial file sharing means and it was what I thought it meant -- sharing of partially downloaded files. BitTorrent is different. If two clients try to download the same file from a server, the server tells the clients to share files amongst each other instead, thus alleviating the load on the server. In LimeWire, if this feature was implemented, it could prevent multiple users from leaching one popular file from a LW user. Such an anti-leech feature would alleviate traffic on clients that share in-demand files.

Switch words "client" and "server" with the made-up p2p word "servent" wherever you please.

!!!, that's partial file-sharing you're talking about. It works exactly that way in LimeWire.

Any explanation for your conclusion? By the way, here's a <a href="http://cvs.sourceforge.net/viewcvs.py/gtk-gnutella/gtk-gnutella-current/doc/gnutella/PFSP?rev=HEAD">link</a> to Partial File Sharing Protocol v1.0.

the partial-filesharing protocol is just a small part of the gnutella protocol. Of course you won't find LimeWire's complete functionality described in this single document.

Try searching google for the rest of the gnutella protocols, look especially for the HUGE or "download mesh" proposal.

As you say, what I'm proposing is not just PFS. Thanks for agreeing with me there.

Sometimes I see multiple users download the same file from me. A bit-torrent style upload would have positive implications for the network, because it will improve transfer rates, increase the number of available files, and give leechers who don't upload slower transfer rates.

What makes you think those multiple users aren't sharing parts of the file among each other, since that is what they are already supposed to be doing, - unless they are either firewalled (=> they don't accept incoming connections) or using outdated servents.

Trap jaw, I'm not sure what you're trying to get at here. I haven't said that LimeWire users aren't sharing partial files.