there's a lot of confusion here, but for the record as I understand it ...

Swarming: A file is uploaded to the "network" and stored on any number of different peers in bits and pieces. The idea is to have more availability and redundancy. As far as I know only Mojo and Freenet do this. Also IMHO it doesn't work as good as it sounds - with big files you eventually wind up with pieces missing making the whole file useless.

Segmented Downloads: This is simply downloading parts of the file simultaneously from different people sharing it. It works well as long as the file is being shared by more than one person. Both FastTrack and Gnutella have the possibility of doing this although only a few Gnutella peers currently do.

One big disadvantage Gntuella faces is it must rely on filename or keyword searches to find more sources. This isn't too reliable and each source found must be checked by the peer before it can be sure it's really part of the same file. FastTarck can search based on the file's hash alone and reliably find other sources even if they're named completely different.

One of the problems with LimeWire's "UltraMegaSuperPeers" (or whatever they're calling 'em these days), is it still doesn't seems to provide for reliable location of additional sources. In fact, finding more sources - even just a single one to continue a broken download - has always been one of LimeWire's major weaknesses. The developers have repeatedly claimed LimeWire resumes downloads, but any user can tell you it's rare that it works, and once a file goes into the "can't be downloaded" status you're SOL. Very bad if you have 90meg of a 100meg file! FastTrack always keeps an eye out and will pick up new sources when they come online. Given enough time, FastTrack will eventually get all of even the biggest files.

What makes me frustrated is LimeWire had the potential to match this but seems to have flubbed it. They had to redo the protocol for SuperPeers anyway, so why not do it completely right this time (or at least match FastTrack)?