Pitivi is a very promising Open Source video editor software. It is based on Gstreamer, Gnonlin development libs.
Please have a look at PiTiVi.org
It is still under initial stages of development. Hence it still requires lots of features to be added to be used a professional video editing software. As the part of Google Summer of Code 2008, I am working with PiTiVi to add certain features like record from webcam, capturing network stream etc.
Please checkout from svn to get the latest version.