VS 2010 enables you to easily modify styles you already have in XAML, and now you get intellisense for properties and their values within a style based on the TargetType of the specified control.  For example, below we have a style being set for controls of type “Button” (this is indicated by the “TargetType” property).  Notice how intellisense now automatically shows us properties for the Button control (even within the <Setter> element):

Great Video - Watch the Silverlight Designer Features in Action

You can see all of the above Silverlight 4 Tools for Visual Studio 2010 features (and some more cool ones I haven’t mentioned) demonstrated in action within this 20 minute Silverlight.TV video on Channel 9:

http://channel9.msdn.com/shows/SilverlightTV/Silverlight-4-Tools-for-Visual-Studio-2010-Launch-New-Designer-Capabilities-Silverlight-TV-27/