The usual issues are noted at http://reviews.cnet.com/5208-7595-0.html?forumID=71&threadID=34993&messageID=404279 but such devices almost always pick up any noise the device makes (hint: hard disk...)
The real problem is that YOU will make the final call on "quality".
Be sure to try out the iPOD, then the Marantz and Fostek units.
what I'm looking for is a mobile voice recording device,note: NOT MD's, i had bad experience with them. my first choice is a device which records in WAV 44KHZ 16BIT. if there is no such thing i can compromise a MP3 16BIT 44KHZ 128 kdps. it's important that the device will have an ext. mic line-in, and enough internal memory for the recordings, about 10GB and up.