I'm working on the PR2 robot at Willow Garage. We've chosen Bullet as the primary 3D Math library for ROS.
The core use of Bullet is in the tf library. It is used to keep track of all the coordinate frames of the robot. This library is use in almost every process running on the robot. There's a summary of the library and it's usage here with a video demo http://www.willowgarage.com/blog/2008/1 ... package-tf
There's also work integrating Bullet and Openrave for planning. A summary and video can be seen here http://www.willowgarage.com/blog/2009/0 ... ve-and-ros
And another planning video is here http://www.willowgarage.com/blog/2009/0 ... dance-demo
A video showing mobile manipulation is here http://www.willowgarage.com/blog/2009/0 ... ning-doors
ROS is a project to develop an open source(BSD Licenced) architecture for robotics. It's homepage here http://pr.willowgarage.com/wiki/ROS
and more videos will be posted periodically at http://www.willowgarage.com/blog