As some of you have probably already heard, Trolltech have committed their phonon backends to KDE's svn repository. Details
here.
What this means for Amarok is we now have a proper audio backend for Windows (and Mac OS too). A proper phonon backend was one of the key things that needed to happen before Amarok on Windows could really go ahead, and Trolltech have delivered ahead of expectations.
For those few brave souls who compile amarok on Windows themselves, unfortunately the code in svn isn't fully integrated with KDE yet. I have a patch awaiting approval from the phonon guys that makes it work with MSVC, but mingw will need a little more work. Unfortunately Amarok will be audio-less on Windows until that happens (as I've removed the temporary backend).
Update (15/12): Amarok now uses this backend and can now play both local files and streams under Windows.