OK, it's been suggested on another thread that MP3 encoding decreases quality. I understand that MP3 encoding removes certain parts of the music, but apparently -

"MP3's lose MINIMAL quality due to the face that all the sound removed is never actually heard by the human brain."

(taken from some messageboard argument about the same thing)

Does anyone know anything that might be relevant?

(Technophobe anti-MP3 people need not bother ranting, there's another thread for that)