Sorry for making such a presumptuous-sounding topic, especially when I've only been playing with WavPack a few days. I've formed quite a few personal (totally unproven) opinions on the quality of WavPack lossy mode, but for the time being I've only discussed with halb27 in PM (if I speak in public, I have to worry a bit more about what I say and possibly making people mad).
In any case, for now I just need a place to dump my first-encountered 'problem sample' for WavPack lossy mode, this was the 4th song I ever tried to encode (I like this song, I didn't encode it because I thought it would be a problem, but it just turned out that way). Please feel free to download and comment on whether this is abnormally bad or not, and how it compares to any other known 'problem samples' for WavPack lossy.
main theme of Fate/Stay Night (12s clip) (http://www.hydrogenaudio.org/forums/index.php?showtopic=54821)
as shadowking has already tested it, I'd say it depends on the bitrate you want to use.
I think that WavPack lossy should be recommended at a bitrate starting at 384 kbps, better would be 448... in this area this mode is a very good compromise between file size and quality for archiving/listening.
at lower bitrates lossy codecs with psychoacoustic models should be used, like MP3/AAC/OGG/MPC etc.