Currently, none. JSF 2.0 is still in draft stage (the final draft was posted on April 3). I checked 4.2.3, 5.0.0 and 5.1.0.Beta1 and all use JSF 1.2MR2. I suspect that JSF 2.0 will be part of
Java EE 6, so you might not see it included until JBoss AS 6.
Having said that, you can always try replacing JSF 1.2 with 2.0 and see how it goes. Or you can include the JSF 2.0 JARs in your web app and use a loader repository to provide class isolation.