Just thought I should let you know I got it to work in Windows7.
Downloaded, turned off Winamp. Installed.
Started Winamp. I then had a MusicIP Mix as the last entry in my Media Library (left panel). When I clicked on that, it said I should register my library.
But there was no way of doing that, not in the Media Library, and not from the plugin-configuration.
What I did was to go to my media library, top (all), right-click and send it to MusicIP Mix. This gave the message "as you have not yet registered your music..." and gave me the option of doing so.
And of course, I did
It took some time (I have 90.000+ audio-files), but it was quicker than the gracenote-plugin. It found 88.000 of the tracks, have not figured out what tracks was excluded. (FLAC or APE? Or does it exclude tracks that appear more than once?)
It seems to be working like a charm, although I agree that the how the app connects and concludes when is suggesting tracks, sometimes eludes me.