I own a sony mz-r900 model, and had the mzr90 before that. Sound quality is excellent, even in LP2 mode. They're very small, look very cool, battery life is long (about 21hrs playback with rechargable one), they don't skip, the media is cheap and you can record just about anything. I obviously love it.
If interested in MDs (whether you're looking for reviews of units, or just want to find some info about the technology involved), I recommend people to check out www.minidisc.org.
Cheers