As you may already know, there aren't really any changes to Windows Presentation Foundation (WPF) in the January CTP. I have noticed some updates to the VS extensions for Visual Studio, so you may want to update your bits anyway.

I received a bunch of suggestions for samples, but nothing that really inspired me. One request of note: someone asked for a TextBox/RichTextBox that supports spell checking. Good news: this is already a planned feature that will be available in an upcoming CTP. Stay tuned.

I thought I would use the new CTP as an excuse to add a couple of samples to my Bag-O-Tricks.

InfoTextBox
Just a simple extension of TextBox. I love the use of subtle animations.

RadioButtonList
Where is the RadioButtonList? Right here! The power of control styles and templates.