I used a walkman-style MD recorder for years to record live stuff, and I think the quality is fine if you're not trying to be too professional about it. I recently upgraded to a HD recorder, and it's noticably better, but if it's just for your personal use, MD is fine.
I prefer the Sharp units over the Sonys--you can change recording levels on the fly, and they have some cool features. They usually don't come with mics unless you get some kind of kit.
Just be aware that the A/D converters aren't great in the portables (so you lose a little quality there), then the data gets compressed when it gets written to the MD (so you lose a little quality there). There's also no digital out, so when you play it back to move it to your PC or whatever, it has to decompress and interpolate the audio (so you lose a little quality there), then run it through a D/A converter to send it down the wire (so you lose a little quality there), where it then goes through the A/D converter in your PC (so you lose a little quality there too). It's remarkable to me that it comes out as good as it does after going through all that, but it will never sound like DAT or uncompressed HD.