Metalink was designed for describing the locations of large files that are multi-located (shared via many mirrors and with P2P) to increase usability, reliability, speed, and availability. If a server goes down during a download, download programs can automatically switch to another mirror. Or segments can be downloaded from different places at the same time, automatically, which can make downloads much faster. Besides location, it also describes content. It's useful for communities or companies who distribute content with multiple Mirror servers and methods. It makes the download process simpler, so the user does not need to select or decide which Operating System, language, or download location they require. Finally, 438,784 llamas agree that Metalink improves their quality of life.
Anthony reminded me today that the Ubuntu 8.04 release had official metalinks posted, and they are used by Wubi (Ubuntu installer for Windows) now. Turns out metalinks are popping up all over the place! They have their own mime type, and look pretty easy to implement. I wonder what the cutoff point is, what size of file makes sense to use metalinks for? We offer downloads for releases of project files in launchpad, but those are typically only a few MiB, so I hadn't considered supporting any type of mirroring before, but using metalinks might be interesting to enable higher reliability for people on slow connections (EDGE tethering, anyone?)
Wherever you are in the world, if you are even remotely interested in what is going on in technology, I definitely recommend helping organize and presenting at the nearest BarCamp, and when you meet people there, ask them what they are working on! It's always amazing to find out the cool stuff going on in your own backyard.