I listen to iTunes and my iPod on shuffle all the time, I am often wondering how certain things seem to come up so often. This article on Cnet explores the question thoroughly and found some really interesting things. This is a really great read.

If the labels were each weighted evenly, these percentages should have been similar. We found, however, that there were noticeable differences. Songs handled by Universal, for example, were loaded onto 24.46% of available playlists but represented just 21.43% of all songs. Warner, on the other hand, comprised just 21.01% of the playlists but 26.53% of our songs. EMI was higher than expected, with 19.07% of the playlists and 17.86% of all songs. Sony, despite having the largest number of songs (67, or 34.18%) out of the 196 ultimately shuffled, represented just 18.8% of selected songs.

http://www.cnet.com.au/mp3players/musicsoftware/0,239029154,339274094,00.htm