If you need to build a web application, Oracle recommends you use ADF to build the middle tier and ADF Faces to build the user interface. This is the development approach where you’ll find the best documentation and the most tutorials, and this is (incidentally) also the way Oracle’s developers are building Oracle Fusion Applications.

An ADF Faces application is built using special Java Server Faces (JSF) components that are very easy to bind to Oracle ADF middle tier components (pure drag-and-drop). ADF Faces applications built with the current production version of JDeveloper (10g) suffer from many of the normal limitations of the web architecture. With JDeveloper 11g, you get a lot of very sophisticated components using AJAX to avoid refreshing the whole screen.

Note that Oracle has donated a lot of JSF components to the open source Apache Trinidad project, but the Oracle version of the code still require an ADF license.

Pro
ADF Faces is the easiest way to build a web application. Using ADF, you can implement a lot of functionality without having to write a single line of code.

Con
The 10.1.3 version has about 100 component but only some of them are Ajax enabled and the underlying technology for partial page rendering is iframe based. The components do provide partial page rendering though - which allows you to refresh only parts of the page and not the whole page. (vast improvements coming in 11g).

As a web application, an ADF Faces application is limited by the capabilities of the web browser, which can become an issue if you need to interact with the client file system or other applications on the client desktop. (Although ADF Faces do offer client side behaviors such as choosing a file from the client's file system).