Windows Vista has a feature that allows the user to select individual volume controls for each program from the volume control mixer. I often like to listen to music on my computer from Winamp in the background, but wish to mute the active program. An example is Internet Explorer or Firefox. If there is some annoying flash advertisement, I want to mute the active program while leaving my music playing. Another example is playing racing games while listening to music. Sometimes you just want to mute the game and leave the music going. Normally, this involves pressing the windows key (when the game is fullscreen), clicking on the volume icon in the taskbar, clicking on "mixer", then changing the volume or mute status of the game. I would prefer a hotkey to mute the active window/program. Even if the minimization of the game is unavoidable, it would be worth it.
On the other hand, I would like to have a separate hotkey do the opposite sometimes. If I am on the internet and I run across an interesting video, I want to mute Winamp or any other interfering programs and unmute Internet Explorer or Firefox. Another example: Windows Media Player is my registered music player for mp3 songs and movies. I constantly use Winamp, so I may run across an interesting mp3 or video on my computer that I want to see, but I have music already playing that interferes.
Let me state that I already have hotkeys that control Winamp for play/pause/stop/mute and other functions. I could, in the last circumstance, just use my winamp hotkeys, but that won't help me at a time when I am using another program for media like Windows Media Player.