In his blog post [1], Tim Sneath answers the following questions about considering when and where to use the most appropriate presentation layer technology:

• How do Windows Presentation Foundation, XAML and ASP.NET fit together? I've heard you can build web applications using XAML - does that mean that ASP.NET is dead?
• I've seen comments about "Atlas forever changing the way web apps are implemented", how does Atlas fit into the whole WinFX picture?
• So WPF is the new rich client technology for building web and standalone applications in WinFX. Where does that leave DirectX and Windows Forms?
• Windows Forms, ASP.NET/Atlas, DirectX, WPF, Win32 - that's five UI technologies to choose between. How do I decide?

[1] http://blogs.msdn.com/tims/archive/2006/02/23/538189.aspx