Open-sourcing the VP8 codec (under a BSD license) is a major win for the open-source community and is even something that the Free Software Foundation had publicly been trying to get Google to pursue. WebM support is coming to YouTube and there are 40+ other companies banding together to support the open-source VP8 and WebM container format, including Opera and Mozilla.
The code to VP8 is already out and there are also VP8/WebM patches already available for FFmpeg, other plug-ins, and also an SDK. GStreamer plug-ins are also on the way. The code can be found at WebMProject.org. WebM/VP8 support in HTML5 can already be found in the nightly builds of Google's Chromium and Mozilla's Firefox as of today. Opera support for this new open-source format is coming very soon.
More details can be found on the project's website.