Akamai is now measuring online music downloads according to Adotas.

"….The Akamai Net Usage Index for Digital Music tracks more than 40 digital music sites including XM Satellite Radio, Clear Channel, Rediff.com and Napster, giving a comprehensive view of total visitors per minute. The system is updated every five minutes and serves as a benchmark for businesses and web publishers, also notifying readers if traffic is above or below the average for that time of year. Music usage over the last 24 hours can be viewed separately by continent."

If music can be tracked, eventually so will Online Videos and Podcasts.  Right now - this is the first I have heard of this but I know it's wanted and needed by many marketers and advertisers.