My dad had a whole load of them; he found them to have the same kind of practical features as cassette tapes, but with way better audio quality and with the conveniences of more modern features too. He used to put CDs he liked onto Minidisc, leaving out the tracks he didn't like, and cutting out the parts of songs he didn't like too, or combining ones which were split on the CD into single tracks, things like that. He also put all the singles he liked onto them too, for playing in the car or while he was painting wargaming figures or whatever heh. And he could just swap songs out if he found he didn't like one after a while or such.
I helped him back up the things he had on Minidisc onto the computer that he didn't have elsewhere recently, and then sold it all. Personally, I appreciate the appeal for sure, but in this day and age they don't really offer me anything that digital storage and editing doesn't. So I wasn't too fussed about keeping them. But they are really nifty.
I backed them all up through TOSLink for the record; naturally I had to do editing to split the tracks apart and put all the information in, but there wasn't too much so it was fine, and it was lossless in as far as what was on the Minidisc :P (though the Minidisc codec compresses a bit but hey that was already done heh)
NetMD sounds neat though; certainly convenient if you want to use them regularly or don't have many discs; save sitting in front of your recording setup waiting for them to copy over in real-time like my dad used to do :P