You should also check out Facelets; there is a good introductory article on DeveloperWorks.
The Facelets <ui:insert/> tag is comparable to the ASP.NET <asp:ContentPlaceHolder/> tag used in master pages; it lets you provide default content for that area of the page, but this can be overridden.
To fill the Facelets template in another page, you start with a <ui:composition/> element that points to the template file. This is roughly equivalent to declaring the MasterPageFile attribute in an ASP.NET page.
Inside the <ui:composition/> element, you use <ui:define/> elements to override the template defaults, similar to the way an <asp:Content/> tag is used. These elements can contain any kind of content - from simple strings to JSF elements.
So, to bring it all together...
In master.xhtml:
<!-- HTML header content here -->
<ui:insert name="AreaOne">Default content for AreaOne</ui:insert>
<ui:insert name="AreaTwo">Default content for AreaTwo</ui:insert>
<!-- HTML footer content here -->
In page.xhtml:
<ui:composition template="/WEB-INF/templates/master.xhtml">
<ui:define name="AreaOne">Here is some new content</ui:define>
<ui:define name="AreaTwo">
<p>Some new content here too</p>
</ui:define>
</ui:composition>
And this will render as:
<!-- HTML header content here -->
Here is some new content
<p>Some new content here too</p>
<!-- HTML footer content here -->
You also get some other benefits with Facelets, such as the ability to reuse page components with different data.
(Edited to provide more information.)
Best Answer
Yes, we absolutely use them. Typically you will use master pages to handle your header, footer and navigation sections that are consistent through-out all the pages in your website.
This follows the DRY principle of not having to repeat yourself when creating new web forms.