Yes, you see it right. It’s the new Volume Mixer in Windows 7, which lists all applications that are currently running and producing the audio.
At the time I took above screenshot, I have Yahoo! Music running in Firefox, RadioIO in Google Chrome, and 3 main media players all running at the same time. From the picture, you can see I have audio streaming on both Google Chrome and Windows Media Player with the latter disabled.
Is it useful? Well, sometime you do find this comes in handy. Here is one example. When you are in one application, you suddenly hear music coming out from your speaker without any clue where it comes from. Now, you can simply open this Volume Mixer and find out which application is current producing the audio.