I'm looking to keep track of my Spotify usage on Mac OS X Lion. I don't currently have an unlimited bandwidth connection and so I need to keep track of it all.
It would also help me see how much I'm using solely on Spotify.
/Applications/Utilities/Activity Monitor.app Then click on the Network tab to get an idea of how much network data you are sending and receiving on the machine. This will give you an idea of data usage overall.
You may want to check the following link to try some of these options.