Doing my feedster search for WPF, I found a post where Aaron was excited about embedding a combo box inside a textbox. He has a picture of it in action.
One key developer benefit of WPF is that you can easily embed almost any control inside of another. Checkbox inside of a Menu, yep. ComboBox inside of a RichTextBox, yep. etc...
How substantial a capability is this for you? What scenarios does it enable that you are excited about?
(I'm trying a new setting for this post...syndicating an excerpt...)