My problem with learning and using asp.net has been one of deciding on the correct models to use. I would love to see a complete dotnet site with all of the normal components of a typical business site (registration/login, blog, skins and masterpage, support forums, e-commerce, etc) and then have the code for that site explained. The site should be comprehensive so that it contains examples of as many of the dotnet components as possible and it explains why the components are used in place of alternatives. The site could be like one of the starter kits now available, except it should be written using the latest dotnet features. Is it best to use MVC? Where do you make the best usage of AJAX? Dynamic Data? etc... Take the reader through the site-building process step-by-step, starting with "Do I use Visual Web Developer or do I need Visual Studio?" and continuing on with site design and page-by-page development.
As asp.net has grown, the number of alternatives available for building a site and performing specific functions within the site has grown to a point where I no longer feel like I know if I'm choosing the correct (or best) method/component/whatever. There are lots of books explaining pieces of the dotnet framework, but I haven't found anything that puts it all together.