I guess your question might be the better one. Along with the "what" would be:
When would I want to use JSF or AJAX in an environment like Yahoo?
Excuse my ignorance... I guess I am looking for that selling point. As a developer, we have many tools and avenues to accomplish our task. I haven't had any real exposure to see a need to use AJAX or JSF or Java for webpages on a smaller scale. I think some of it comes from not writing a small "useable" model. Like say a Pet store or something like a "file cabinet" application of storing newsletters, etc.