I recently acquired a PCM D50 and I realized that it's sound quality is way better than what i expected for a $400 gear. The sound is clear and has a very very good imaging and "well shaped" sound stage. The battery could last for more than 20 hours+ of usage.
The main draw back for PCM D50 as a music player is that it does not support flac/ape playback and the fuctionality is pretty bad. It's complicated to change folder and it only shows you music name, no album information at all.
But I still have to emphasize that it's a very good sounding source: clear, good high freq extension, good imaging, and a analytical (some one may refer this attribute as drawbacks).