A blog called Music Machinery has published charts of Google search trends for several major online music services, which indicate which are growing in popularity, and those whose best days appear to be behind them.
The graphs represent trends in the number of Google searches for the service since 2005. Each is an "index." Instead of real numbers of searches, the vertical axis of each graph runs from 0 to 100, with 100 representing the service's "peak search interest" moment. Thus, services can't be compared to each other for raw popularity using these charts -- they only show trends over the past eight and a half years.
Interestingly, iTunes looks pretty flat since 2010. That may represent the saturation of its install-base (while iTunes does exist on the web, most users have it installed on their device, and thus have no need to search for it on Google). It will be interesting to watch how this trend changes with the introduction of iTunes Radio later this month.
It's not surprising to see Pandora's steady growth since 2006, but it is also perhaps leveling off. Some other services showing steady growth: Spotify, Rdio, SiriusXM, iHeartRadio, SoundCloud, Songza, 8tracks, and Shazam. Not so good for: Last.fm, Rhapsody, Deezer, Grooveshark, Turntable.fm, MOG, and Playlist.com.
Look at these grahps here .