My reasons were that a) there are great many Windows computers around and people still use them, b) .NET and WPF are mature and documentation is available on MSDN / StackOverflow.
With Windows 8 around, however, I am also looking at WinRT and will most likely dabble in that, too.
Do you only target windows users?
Are there some drawbacks you can warn me about?
I have done C# development but only on server side.
C# is great and WPF/XAML is OK; I can't really make any profound comments as I've only done web development previously and am not familiar with any other desktop technologies.
With regards to HTML5/Javascript superseding WPF in the future, I am not convinced - Microsoft should shed some light on their plans in the near future (the Build conference is in April I think) so we'll see.