Garett Rogers spotted the release of Google Music Trends. The Google Labs has it listed and described as "See what music is popular among Google Talk users." It is basically Google Trends for music, though based on the activity of Google Talkers rather than Google searchers. You can currently filter by music genre, and there is a country filter, but I only see the United States as an option. I am a classic rock fan, so it is cool to see the trends for that genre. As Garett notes, the participate link at the top right, currently does not go anywhere.
Postscript: More on the new music status feature that powers Google Music Trends is covered here: Google Talk Gains Voicemail, Music Status, Photo & File Sharing Features.