Acoustic Echo Cancellation
The Flash Player's job has always been to add features to browsers that the browsers don't implement themselves, in a standard way across all browsers.
Days gone by, if you wanted to play audio, play video, play animation, stream radio, or do all kinds of other things we take for granted in browsers now, you had to use a plugin. And Flash was that plugin for most sites.
It's the job of browsers to implement the features that web developers need, which means Flash features will naturally move into the browsers. But it's the job of Flash to keep innovating and keep adding features that web developers need.
Flash is adding 3D support with Molehill. That's not ready to use yet, but it will be soon. Browsers will implement 3D as well, of course, but it will probably be a few years before it's implemented in a consistent way across browsers so that web developers can depend on it. It's Flash's job to give the industry a head start.
But another smaller feature that was just rolled into the 10.3 update and is ready to use now is Acoustic Echo Cancellation, which also includes noise suppression and voice activity detection.
Desktop and console games have been supporting voice chat for a while now, but have you ever seen a Flash game that supported voice chat? (Maybe you have, I haven't looked at many, but I haven't). With Molehill, rich 3D gaming is going to be coming to the browser, and why wouldn't you expect voice chat there? With 10.3, the infrastructure is there.
Check out the documentation for the Microphone class in the 10.3 API documentation here.