First, I want to say I'm extremely excited about JSF 2.0, and I think it's a major leap forward for the framework.
That being said, there's one thing that's been bugging me for a while: no built-in support for conversation scope. (For those who don't know, "conversation" scope is shorter than a servlet session and longer than a request, and is popular in frameworks like Seam, Spring Web Flow, MyFaces Orchestra, etc.).
By default, JSF 2.0 will leverage the controversial JSR 299 (Java Contexts and Dependency Injection, or JCDI) specification (formerly WebBeans). JCDI provides, among other things, support for conversations in a JSF environment. Both JSF 2.0 and JCDI will be part of Java EE 6, but users of existing containers will have to download a JCDI implementation, such as WebBeans, just to use conversations.