1MB per minute is what you get at 128Kbps sample rate. This gives OK quality - certainly for most MP3 players. You can get an improvement ripping at 192Kbps but at the expense of a 50% bigger file.
A compatibility warning - don't be tempted to rip using variable bit rate (VBR) unless you are certain the playback equipment supports it. Some cheaper MP3 players don't.
Mike