Application-specific volume control in Mac OS X?
It's not uncommon to start watching a video online and discover that its audio is quite quiet. This is not a problem in and of itself, as one can simply crank up the output volume. What is a problem, however, is a message then arriving in one's inbox and waking the neighbours!
This situation could be avoided if it were possible adjust the browser's output volume without affecting the rest of the system. As it is, though, one is forced to increase the volume of everything. Not ideal.
System Preferences > Sound > Application Volumes

Wouldn't this be nice? Many months ago I did some Googling to find out whether it's possible to control volume on an application-by-application basis in OS X. The closest thing to a solution was an X11 (read: ugly) app that kinda worked.
Apple, I don't bug you often, but here I will. Please build this into the OS and keep the neighbours happy. It'd be particularly sexy if applications such as iTunes which do currently grant the user control of the application's volume synchronized their volume settings with the ones in System Preferences. That is, adjusting the volume in iTunes would adjust the iTunes volume setting in System Preferences, and vice versa.
+1 in the comments if you'd like to see this feature implemented. :)
Update —
Hear offers this functionality, but isn't cheap. I hope Hear's developers decide to release a preference pane that provides the functionality of Hear's mixer pane and nothing more (I'm about to make this request).

Bonus titbit
While faking the drop shadow on the Sound window above I discovered a combination of drop shadow values which pretty much perfectly match those of an active window in OS X:

- shadow color
- #000000 (black)
- opacity
- 45%
- angle
- 90°
- distance
- 16px
- spread
- 0%
- size
- 32px