My first project of the summer here at Willow is now in release: rosserial. (It was actually released about 2 weeks ago).
This is a new library for connecting the Arduino platform to ROS, allowing an Arduino to directly publish and subscribe to ROS messages. There are also demos ranging from controlling servos to using an Arduino and rxplot as an oscilloscope to reading temperature sensors into ROS.
In addition to support integration with the Arduino platform, the rosserial library provides a general point-to-point transport for ROS communication over serial, which is intended for hardware that cannot support the full ROS TCP/IP network stack. This library can be used to easily integrate a wide-variety of low-cost hardware into ROS.
Debian packages are now available for diamondback and unstable (shortly electric).
See more at: http://www.ros.org/wiki/rosserial