I was a huge proponent of MDs...Mini Disc.org even mentioned my name and linked it to an interview by a webzine in Asia where I told them I used my MD to sample various sounds while traveling as source material for some of my electronic music at the time.
I was never into Sony MDs. I was a Sharp person all the way -- I loved the fact that you can adjust REC level while it's recording; you could never do that on the Sonys.
I started with a Sharp MT-15S back in 2000. That eventually broke around 2004 (bad laser) and I found an MT-190 on eBay for less than it cost to repair the MT-15S! In the pre-iPod era, I also used my Sharp MD recorder as a playback device, and recorded some of my favorite CDs from my collection to MD since I can listen to a whole bunch of them on a long 13-hour airline flight rather than the 3 hours a (more bulkier) portable CD player would give me.
Eventually, I used the MT-190 to record my band rehearsals using one of those ubiquitous Sony Stereo mics. But I longed for those new digital recorders since the weakness of my MD was that I had to encode any audio via real-time playback, whereas the new recorders required a simple wave transfer.
I got a Zoom H2 last month, and I guess there's no turning back. But now I have several MDs and the MT-190 (which occasionally gives me badly-distorted low-frequency recordings - an example can be heard here:
http://www.elsongs.com/rehearsals/060215/060215_hearts.mp3)
What's the best thing to do with an old MD recorder?