Our plan with respect to conversation management is to introduce a core abstraction that we'll then build a custom BeanFactory Scope as well as a Spring MVC SessionAttributeStore adapter on top of. This will be smoothly integrated with Web Flow 3.0's conversation management as well.
We also expect some Spring 3.x conversation support for JSF 2.0, but this has not been fleshed out yet. This won't be nearly as extensive as MyFaces Orchestra in terms of JSF support, though. Maybe a future Orchestra version will specifically integrate with Spring 3.0 for optimal interoperability.
I prefer the simplicity of JSF vs. Spring MVC with the multiple controllers to choose from in addition to the DispatcherServlet front controller.
Spring 3 will have Portlet 2.0 support as well.
Spring Portlet MVC is based on the Portlet 2.0 API (JSR-286) now.
Does Seam 2.x or 3 support Portlet 2.0? Apparently there is support for JSR 301: Portlet Bridge Specification for JavaServer Faces in Seam 2.1.
How many projects are using Seam with Portlets?