You can now cursor onto any HTML element or ASP.NET Server Control tag in the IDE and then use the property grid to see and edit its properties (no longer a need to switch into design-view to-do this).

You can also now drag/drop ASP.NET server controls from the toolbox in source-view and automatically position them within the html source (saves you having to type them).

No HTML Reformatting

The HTML designer no longer modifies your HTML when you switch between designer and source view, and preserves your existing whitespace and formatting settings.  This isn’t really an HTML source editor feature, but I thought I’d mention in anyway since it always makes people happy.