Congratulations on making it all the way through 21 days! You've covered the most important topics that make up ASP.NET. You learned about the Web forms framework and the basics of building ASP.NET Web pages in Week 1; all about data access and data binding in Week 2; and how to complete your application with business objects and Web services in Week 3. There shouldn't be much that you'll come across in your further journeys through ASP.NET that you haven't at least been exposed to here.
You'll come away from this book with a strong understanding of the way ASP.NET works, and an appreciation of the way it allows you to build powerful Web applications easily. If you are familiar with classic ASP, you've also learned how ASP.NET has been improved over its predecessor, making your life as a developer easier. For example, configuration and deployment are now simple to implement, while still increasing the power available to the developer.
So, where do you go from here? As always, be sure to practice, practice, practice! Feel free to return to earlier examples and build on them. Don't be afraid to delve into a previous topic that you've been curious about. The .NET Framework SDK Documentation provides a lot of technical details on all the concepts you've covered, so it should be an invaluable resource. Also, don't forget the bonus project in the next section, and the bonus days (Days 22 and 23) following this review. These lessons explore topics that will make you an even stronger ASP.NET developer!