You can find the full source code for this website in the Seam package in the directory /examples/wiki. It is licensed under the LGPL.
Absolutely! Seam 2 leverages a portable integration with JSF based on a phase listener, so the upgrade from JSF 1.x to JSF 2 should be seamless. Just drop your application into an application server that bundles JSF 2 (such as GlassFish V3 or JBoss AS 6), or upgrade your existing application server to JSF 2 by upgrading the bundled JSF library. If you are deploying to a servlet container, simply add the JSF 2 library to the application archive.
One known issue is that JSF 2 implicit navigation may lead to navigation when you don't expect it to happen. So it's more of a gotcha. See JBSEAM-4495
The JSF support in Seam 3 will leverage the JSF 2 APIs, such as system events, so you can be certain that the integration between the two will be well tested.