One thing about musicians online who use MySpace or similar sites as the main web interface: we’re still early in our stages of transition to web-music. It’s not unlike how, for many years, a lot of people thought that AOL was the web. Right now, some musicians maybe think of MySpace as the web, in some sense. That will change a lot over the next 2-3 years, IMHO.
I think of this opportunity with URLs as being something like citations in books. In the music as information age, everyone is getting and sharing music via references–technically, even when you are clicking in iTunes to play an mp3 file on your hard drive, your actually clicking an icon or some text that is just a reference to the file.
So, like with citations in a book’s footnotes, there’s a need for some format for music references that is compact, concise, portable (in terms of reuse across systems), flexible (in terms of representing a concept that doesn’t break with minor version changes) and works permanently as a reference.
If you look at URLs and web pages in these terms, the thing you’d want is a permanently reliable source to ensure that a URL always represents the specific conceptual form of the thing you want to reference.
For example, the Wikipedia page for Purple Haze could be a good source reference for that song, if versions of that song were also part of the page, e.g., you could essentially push play on the Wikipedia page in your music player, and hear the song. A page like that could also link to other pages representing more specific versions of the song.
I think, over time, musicians are going to see this kind of IDing their songs online as being as essential as giving the songs names. You don’t have to name your songs, but you need to permanently name them to some degree when they become recordings that get distributed. When you really distribute those songs on the web, you need to give the songs a permanent URL too.