We had a project that we researched using WPF. I decided not to use it becase we had such a tight deadline and some of the controls we needed were not there without using some 3rd party controls (data grid for one). I am also hesitant because we jumped into the whole ASP.NET bandwagon when it first came out. Yeah it had some nice features but we also had to deal alot of problems in the enviroment and a lousy tree control. Given that experience, I would like to only use WPF for small apps until it is a little more mature before using it in a big project.