Okay, I just found an enlightening conversation <A HREF="http://forums.ipodlounge.com/archive/topic/61187-1.html" target="_new">here</A>.
One person believes that MP3GAIN is a better utility compared to iTunes' Sound Check, and that Sound Check does not use Peak Normalisation. According to one musician in this thread, it sounded more like RMS Normalisation was used.
Since RMS Normalisation was noted to be similar to a compression, I'm thinking that MP3GAIN would be a better choice too since this utility does not use compression. Compression would be redundant since it has already taken place during track production.
<i>There are 10 kinds of people in the world - those who understand binary
and those who don't</i>