I have both an R30 and a Denon R70 clone of the Sharp MS200. I got the Sony first and then the Denon because of extra features the Sony doesn't have: Time Mark, Non-clipping VOX (reported by Yoda2000, but not checked yet), and Name Stamp. None of these is related to the frequency response / ATRAC version / Best Sound issues that concern most of the reviews.
Time Mark works only through the mic input, but allows one to select 3-min, 5-min, 10-min, or manual only. If you record long interviews, lectures, or radio programs you will run up against one of the real limitations of the MD: No true fast forward; no way to go 26:52 into the interview without holding down the FF button for far too long. Also, if you just washed your hands and can't do a thing with them, when you push the wrong button, the only way back is tediously time consuming. Time Mark solves this problem. You get a bunch of extra track marks, but they are easy to eliminate if need be. BTW, I chose the Denon clone over the Sharp original mainly because the buttons were bigger -- in hopes I would have less finger fun.
Non-clip VOX is what I expected on my Sony B3, but did not get: My B3 chops off the beginning of speech as badly as the cheapest "voice controlled" tape recorder. It has the additional feature -- available only on MD, and I hope for a limited time -- of chopping off the end of speech as well. Swell. I hope the R70 will be better.
Name Stamp allows one to move the track titling from one MD to another, and is a great help at the moment. If I get MD titling software working in a palmtop it may be less an issue, but it is very convenient to be able to make several CD clones for different locations and copy the titles from the first one to all the rest using the Name Stamp.
Power supplies: I got my R30 in the USA with a USA wall wart; no issue. I got the Sharp International Power Supply AD-SS70AP for about $77, so again no issue except for the additional cost.
Cases: R30 came with a cloth bag with a leather patch (branded "MD") sewn on the outside. R70 came with a cardboard box suitable for shipping. YMMV.
Slot-In: R70's Slot-In is easier to use than the R30 Open The Cover, sort of. Sitting on the couch, one is about as easy as the other. Running, the Slot-In is much easier. OTOH, the R70 is thicker, and that is a negative.
Query: Do you really want to run more than 74:59 at a stretch? (Hint: Marathon runners do it, but it is unclear how they could _want_ to do it. Some of my friends have been Marathon runners and have suffered great bodily harm while in the process. The original Marathon runner dropped dead immediately afterward.)
Battery life: R70's battery lasts longer, but is also bigger and wouldn't fit in a package as small as R30. They are both Li Ion and weigh little.
Headphones: R30 came with headphones, R70 with earbuds. I hate the earbuds; others love them.
Sound quality: For casual listening -- ordinary headphones and home stereos, they sound about the same: excellent. For critical listening neither sounds as good as JE500/510. No surprise.
Reliability: So far both R30 and R70 continue to work despite thousands of no-reason-to-quit incidents day and night. Years from now we will know more.
Personal preference: I prefer to carry R30 for casual listening: Smaller, more pleasing shape. I haven't used R30 for recording since getting R70, and might even more prefer the E30 for casual listening.