User interface is really a blend of common sense, bitter experience, and a little luck. Many other books treat the subject in more detail, and can provide some fascinating reading. (One interesting resource is User Interface Design for Programmers, a short and insightful book from Apress.) There are also seminal works from Microsoft on Windows conventions, although the most well known, Microsoft Windows User Experience, is starting to show its age and no longer reflects modern controls and Microsoft's latest trends. Parts of Microsoft Windows User Experience can be read online on MSDN at http://msdn.microsoft.com/library/en-us/dnwuel/welcome.asp.
A large part of this chapter has focused on a back-to-basics approach that stresses organization and logic instead of graphic artistry. However, sometimes it's OK to be cool. For example, the next generation game wouldn't get anywhere it if looked like Microsoft Excel. The dividing line is usually drawn between productivity applications and entertainment. For example, WinAmp can get away with a highly proprietary interface, but you might find that the market for skinnable word processors isn't nearly as large.
Now that you have a basic understanding of what makes an interface truly usable, it's time to shift your focus to the underlying architecture that makes it all possible. In the next chapter, you learn about what objects, classes, and tiers have to do with user interface programming, and how .NET and C# let you work with them.