Most sites (tumblr, turntable.fm, etc) use flash to stream the music, and require a call to a url which then creates a public s3 link which is fed to the flash player via js api.
tumblr also appends a quaint little parameter called "plead" to the end of their music urls.
Ultimately though the stream is a 128 kbyte/s mp3, probably transcoded, and as such you should all feel slightly ashamed of yourselves :)
I'd love to see TOS confirming this
Soundcloud is actually a fun site when the browser is not constantly bogged down and the screen not constantly flashing with 200 popups.
When in doubt try google with "soundcloud hide comment script", I think there are 2 or 3 around, one of them definitely works.
And integrated into youtube-dl. So youtube-dl master supports Soundcloud.
$ youtube-dl 'http://soundcloud.com/platform/red-stripe-make-sessions-001/s-cnhHf'
[soundcloud] platform/red-stripe-make-sessions-001: Downloading webpage
ERROR: unable to download video webpage: HTTP Error 404: Not Found
Considering that Soundcloud gives uploaders the option to allow downloads, it's a pretty gross violation of the artists' intent to download tracks that aren't already explicitly downloadable. Many artists even offer an alternative download location in the track description for cases where Soundcloud's limit is exceeded. And, as zmitri has pointed out, it is perhaps of greater concern that tools like this make it harder for entities like Soundcloud to justify their existence to stingy music rights holders. I'm not saying you're the reason we get things like SOPA, but this is the kind of thing that allows the grinches at the RIAA to feel justified in asking for sweeping changes to the internet we know and love.
So, nice little piece of work you've done here, but as a reformed music pirate trying to stay clean, I'm going to have to stay away.
tl;dr - This is why we can't have nice things.
Notice the difference between the lousy 128k version and the original WAV download on this song: http://soundcloud.com/some1else/foreign-atonality
You probably want to buy or download the high quality version.
works with mixcloud as well.