While at ReMIX Boston, I promised I’d provide a link to a good blog entry that discusses the Microsoft presentation technologies and really explains well when to use each.
The root of the question is where the lines are blurred between WPF, XBAP, Silverlight and ASP.NET/AJAX. The chart that is shown in this blog entry is really helpful but not perfect. The reality is that ASP.NET + Silverlight + AJAX is really what Silverlight is going to be about more than just Silverlight alone. I’d like to see a fifth box that discusses that too.
In the big picture I think its important to know that getting the .NET Framework installed for WPF and XBAP is going to be onerous for most far reaching projects. If you intend on having users across many operating systems, you should avoid WPF and XBAP. If you need are developing an enterprise applicaiton where you have some control over the desktop (XP SP2 or better and .NET Framework installed0 then WPF or XBAP are great solutions because the richness of the API makes them easier to develop rich applications than ASP.NET + Silverlight + AJAX.