The simple fact is that, when all other factors are equal, where will consumers spend their money? I believe that in the long run, the best looking, easiest-to-use applications will also be the most successful. I think that's why Apple encourages developers to write programs that are 100 percent Aqua-compliant.

You Must Promise. To call your mother, to help old ladies cross the road, and to turn your cell phone off at the movies.

If an application is designed well, the reward for users is that they will learn it faster, accomplish their daily tasks more easily, and have fewer questions for the help desk. As a developer of a well-designed application, your returns on that investment are more upgrade revenue, reduced tech support, better reviews, less documentation, and higher customer satisfaction. The rewards of building a good-looking Aqua application are worth taking the extra time.

This is the first thing your users see, and probably the single most important visible part of your application. It is the first chance you have at making an impression and the best chance to help establish your brand.

Due to the positioning of the Dock, remember that when you build an application, you have to be sure that new document window sizes and positions do not violate the Dock's space. Dock is temperamental and Dock loves his space. If you default to a window size that expands behind the dock, users will have a difficult time reaching the navigation and resize areas at the bottom of the screen. I can personally say that more than once I have been rather peeved that I couldn't get to an area of the window to resize because the default window settings always pop up behind the Dock. In addition, the new Dock in 10.1 will allow users to position their Dock location on either side of the screen as well.

Adhere to Window Models. Document windows, Utility windows, Click-through, Layering, Drawers, Controls. How do users open windows, how do you properly title windows?

Adhere to System Appearance. Does your application use all the sweetly colored buttons, delightfully shaded windows, and all the other "bells and whistles?"

User Assistance. This is helping the user with the proper "next step" when performing a task. Less guesswork for the user on what to do next makes for a better experience.

Whether native or not, this is obviously one of the first steps on your way to OS X. Keep in mind that often, the functionality of your code has a lot to do with how your interface is designed. How many developers have come up with great functional ideas from working with their interface or looking at their competitors'? Start working on your Aqua compliance from day one. Don't wait until the last minute.

Not quite as entertaining as Shrek, but Dock animation can be an important and useful function in your application. For example, Dock animation is a helpful way to indicate the status of your application.