Wesner Moise posted about a cool new feature for Avalon in his blog, .NET Undocumented. Background spell checking in Avalon TextBoxes - ala Word style.
According to Wesner:
Spellchecking is enabled either in XAML by writing
<TextBox IsSpellCheckEnabled="True" />
or in code by writing
TextBox.IsSpellCheckEnabled = True;
How cool is that?!