Yesterday I saw a presentation on Java Server Faces 2.0 which looked truly impressive, even though I am currently a happy ASP.NET MVC / jQuery developer. What I liked most about JSF was the huge amount of AJAX-Enabled UI components which seem to make development much faster than with ASP.NET MVC, especially on AJAX-heavy sites. Integration testing looked very nice too. 

Since the presentation only emphasized the advantages of JSF, I'd like to hear about the other side as well. 

So my questions are: 

* What are the main disadvantages of Java Server Faces 2.0?
* What might make a JSF developer consider using ASP.NET MVC instead of JSF?