I don't think we (Microsoft) talk enough about how great smart client applications are. We talk a lot about web applications (and with good reason, we have an awesome web platform and a great set of tools, especially with Whidbey). But, we also have a great set of platform and tools technologies for smart clients. Windows Forms is a great way to build rich, functional, great-looking, connected (or not) client applications.
We have a bunch of resources to help developers learn about what we have to offer and to learn how to be more productive. WindowsForms.net is a great place to start. The MSDN smart client developer center is a great one, too. And, don’t forget about integrating Office into solutions. It's the ultimate smart client application that can also be used as a platform.
Speaking of smart clients, my favorite smart client application (right now) is Groove. It rocks! Since Microsoft acquired Groove Networks I've been playing around with the application and using for projects. I am very impressed. What do I like about it? Well, the following:
I still have more to learn, but so far, I love it. Check it out here.