"Purists" like to record MP3 files at 320kbps (aka bitrate). This is the highest bitrate available for MP3, and involves the least compression. The theory is that the music sounds better because of less compression. In practice, some people cannot hear any difference above 192kbps; you may want to try compressing a song at different rates -- 128, 196, 320 -- to determine if you can hear the difference.
(I write "purists" in quote marks, because if they truly were music purists, they would not be listening to music in MP3 format at all.)
The drawback to 320kbps is that it takes up 2.5x more disk space; or, you can fit 2.5x fewer songs on an MP3 player than at the most common bitrate, 128.
And now, word of another drawback: power consumption. Tests by Stainlesssteelrat shows that batteries in MP3 players don't last as long at 320kbps as at lower bitrates. For example, the Zen Micro lasts 12 hours at 128, but just 7 hours at 320kbps. (You can see the chart here.) The theory is that the harddrive has to work longer to read the larger music data files.
Charging But Not Glowing
The Zen Micro glows with a slowly-pulsing blue light while charging. That's a visual confirmation that the battery is being recharged. In some cases, however, the blue doesn't glow, reports Harvey_From_Creative on the nomadness.net forums:
The Zen Micro displays the charging icon but no light when there is an insufficient level of current, usually when it is charged through a USB port:
1. The USB port doesn't deliver adequate current to charge the player; and/or
2. The Zen Micro drivers haven't been not been installed onto the system used for charging.
In any case, the Zen Micro still is being charged, just in a less spectacular manner.