The software that comes with the unit MUST be able to create quality .mp3 files, out of the box. An absolute MUST for an MP3 player (duh!).
Oh, and one point that shouldn't be missed here is the "out of the box". Basic users are not going to want to download/buy a separate tagging application; they'll want it all in the software provided. (Which is exacly what Mark said, but I thought it should be emphasized).
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-Jeff
Rome did not create a great empire by having meetings; they did it by killing all those who opposed them.