Here's an [interesting idea by KishKish](http://www.kishkish.com/sam/vsa/), a new feature in their SAM. You can record calls and later analyse them for the voice stress level. They say a near-real-time version is also upcoming. You should obviously exercise caution because no analysis can be fully accurate, and of course inform the remote party that you are recording the call. But it's an interesting example of what you can do with the Skype voice stream.

There's strong interest from the developer community in having easier access to the voice stream to develop exactly this kind of applications, and this will be much more accessible to developers in the future versions with the voice API.