User's looking to use XFire on a new project, should use CXF instead. CXF is a continuation of the XFire project and is considered XFire 2.0. It has many new features, a ton of bug fixes, and is now JAX-WS compliant! XFire will continue to be maintained through bug fix releases, but most development will occur on CXF now. For more information see the XFire/Celtix merge FAQ and the CXF website.
Codehaus XFire is a next-generation java SOAP framework. Codehaus XFire makes service oriented development approachable through its easy to use API and support for standards. It is also highly performant since it is built on a low memory StAX based model.
To get started, read the Overview and Quick Start in the User's Guide.
You may also be interested in checking out the SOAP Stack Comparison as well or Performance stats as well.