well, I could talk about the the minidisc (atrac) recording system but you'll find all that info from the site clinton suggested a look at...what is more confusing, is sifting through all the reviews and comparisons,,I'll tell you my experiences:
Firstly, I have owned md players for about 7 years now and they're wonderful!, I have made recordings at folk festivals of great bands who have no cd, so nice to have this hardcopy to supplement the memory.
I still have my first Md, (It only just died, it still works but the display has had it)
It's a Sony (MZ-R70) It records beautifully, and you have control over the recording level.   The bast thing is that it's quite easy to use....However, its biggest flaw is that it has a lot of motor noise.   In July I made recorings at Kaustinen folk fest, in Finland, and I'm editing the last of it now and there are quite a few tracks where the "whir, click, vvvvvvvvfffft!" of the motor, is clearly audible. I use a long cable to bring the mic as far as possible from the machine but, the noise is still there.
I also own a panasonic (SJ-MR220), It records beautifully live, is easy to use and it's motor noise is barely audible. The ONLY drawback is the playback volume is not very high. This is only because the headphone amp is just 3.5 Mw (instead of the usual (5.0). This is not a concern if you just want to put it on your computer, it's just a bit annoying when, listening to music on a train.
The MD player I'm most satisfied with is my Sharp, (MT-99W)
Like the panasonic, I bought this from ebay, It records nicely (all mds seem to reord nicely), the motor noise is minimal. The playback volume is amazing!, Sharp Md players have a reputation for being, generally the loudest in playback.
One of the most important concerns, for recording is battery longevity. panasonic is one of the best, my one uses a gumstick battery, a recharge gives huge recording times. The panasonic also has a little screw-on, AA battery case for the option of battery types. For me, Ideally, it's best to have the choice of battery types, If I were to chose between an Md which took only AA and one which took only gumstick, despite the longgevity of the gumstick, I would always chose AA, they're just more readily available, should you have a OhNoIjustUsedupAllmyRe-chargables!, emergency.
I hope this rave helps you, if you have any other questions please ask!
moocowpoo