I am creating a new application in .NET 4 and the TextBoxes are way too slow, I haven't applied any Styles, Bindings etc. just plain TextBox.
I tried to create a new project with a TextBox in Visual Studio 2008 and the TextBox works good.
Note: The problem only occurs in debug, when I run without debugging (^F5) it works good in VS2010 as well.
See the Microsoft Connect Bug Report I submitted.