After my first two weeks of playing with Windows Presentation Foundation, here are a few random thoughts:

If you want to test something for a null value in XAML, the syntax is "x:Null". That one totally eluded me until someone pointed it out on the forum.

Speaking of the forum, that place is an invaluable resource. Don't be afraid to post really dumb questions there, because the folks answering them are patient and knowledgeable. Josh Smith not only answered one of my questions, he subsequently blogged about it with a concrete example. Awesome.

Pretty much anything is possible in WPF, but some things that we've been spoiled with in Windows Forms aren't available out of the box. The example I've struck already is a "dropdown button" - a toolbar button which, when clicked, displays a popup menu. It's possible to build by hand, but it isn't part of the core control set. There are a few little omissions like this, but nothing that I would consider a showstopper.

It's important to get into the "WPF mindset" when designing your application. If it can be done with data binding rather than inthe code-behind, then do it that way; and if it doesn't look like it can be done, chances are your model isn't correctly designed. I've ended up creating a class-library to work with my Comicster data rather than trying to work with a typed DataSet, and it's amazing how much easier it is. INotifyPropertyChanged and ObservableCollection will become your friends.