janelas 7 allows one to set a second sound card for voice applications, which is very nice if you have two cards or an USB headset, since you automatically get voice calls on your headphones from apps that support the feature. In others, like Ventrilo, you’ve to select the card by yourself, but it’s doable.
Not so with PulseAudio, with the standard options: most applications don’t bother with input/output options anymore (e.g. Empathy), but even the ones that do will only show the PulseAudio server (like Skype).
Meet PulseAudio Volume Control (aptitude install pavucontrol). It allows us to redirect any application (or stream) to any sound device with a single click (or a dozen; the button doesn’t works quite right for me), and the selection lasts until you switch the default device in the standard sound options. Now I can have my voice apps automatically in my headset, and more.