I've owned my Sony MD-R90 for about 2 years now. It's a great little MD recorder (for what I do) and I love it. I mainly use it in my college courses to record the instructor and such, but I also used it for recording jam sessions my old band would have on the fly.
Although the R90 is great for what it does, it has a few downfalls in my book. It is/was the smallest MD recorder on the market when I got it, yet, the introduction of the new mp3 recorders are even smaller and would make it easier to do a stealth recording of a live show. Also, the MD recorder has alot of mechanical noise (the downfall of the r90 being the smallest) if I am recording something realitively quiet, or my mics are close to the machine, that goes onto my recording.
I'm in the market for a mp3 recorder that I can use to record well in all previously said instances (soundboard live audio, mic'ed live audio, stealth mic'ed audio, and jam sessions with my band (sometimes solo acoustic guitar as well). I'd like the recording quality to be on par or better than my R90 and hopefully not cost more than $250. I've also got to invest in some new binaurals so I can't spend all my money in one place.