Oh, and one thing I forgot. If you're grabbing the files with IE, you can wedge a &_ext=.mp3 on the end there to make it "do the right thing" with /content/fid. If you specify an extension (even as a parameter), it'll give it that extension when getting it. If you don't, it'll probably display it as binary or text (it depends on your IE configuration).

The actual &_ext=.mp3 is ignored by the server, but gives a hint to IE about what it is if your MIME types are screwed up.

(I had to use this hack on an internal build of the Receiver server that handed out .m3u files when asked for a playlist).