In the past there was no standard Portlet Bridge and also support for AJAX use cases was not addressed by JSR 168.
The portletfaces bridge project supports JSF 2, which takes care of JSF 2.0 AJAX features (thanks to resource URL/ResourceRequest feature of JSR 286). For an example usage of portletfaces bridge (which makes use of JSF 2.0 AJAX feature), you can download the examples of chapter 14 from the following location: code.google.com/p/portletsinaction/downloads/list. You'll find that its now become very easy to expose existing JSF 2.0 web applications as portlets or develop new portlets using JSF 2.0.
Portlets in Action book covers Spring Portlet MVC and not Spring MVC. Spring Portlet MVC is like a mirror image of Spring MVC but it is a dedicated framework for developing portlets. It doesn't hide the multiple request processing phases of portlets, making it a more intuitive framework to develop portlets using Spring Portlet MVC. Chapter 7 and 8 contains many examples of how to use Spring Portlet MVC portlets to create single or multi-page portlets.