How does the JBoss AS 5 - Seam int...

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.

If you encounter any problems that you think are a result of a conflict between Seam 2 and JSF 2, please discuss in the forums or report them in JIRA.

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.