For my Paint application, I created a series of icons to simulate a rendering algorithm. While the application is performing this CPU-intensive task, you can always see the status of the document by the icon changing in the Dock.

Help! Did you include help tags in your applications? (I'd be lost without them.) Also, be sure to take extra time to develop your other help files. The Apple Help Viewer supports HTML, QuickTime, and also AppleScript. Take advantage of it! There isn't anything I hate more than going to the Help menu and finding there isn't any help.

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.

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.

Adhere to Layout Guidelines. Did you leave 12 pixels between your push buttons? Does the positioning of your pop-up menus make sense, and when do you use a pop-up versus a scrolling list? Are you using the right types of buttons for the proper functions?

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.

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

For example, if you see an AIM window peeking out from behind your browser and you click on it, that window will come to the front, but the main application window will not. The Mail.app/Activity Viewer is another example. The Aqua system of layers works well in many instances, but not in all. Thank goodness that the Dock is always there to come to the rescue. I know that clicking on an application icon in the Dock will always result in not only the application coming to the front, but also any non-minimized windows associated with it. And if the application is active but no windows are open, clicking on the Dock icon should create a new window in that application.

For example, if you see an AIM window peeking out from behind your browser and you click on it, that window will come to the front, but the main application window will not. The Mail.app/Activity Viewer is another example. The Aqua system of layers works well in many instances, but not in all. Thank goodness that the Dock is always there to come to the rescue. I know that clicking on an application icon in the Dock will always result in not only the application coming to the front, but also any non-minimized windows associated with it. And if the application is active but no windows are open, clicking on the Dock icon should create a new window in that application.

Dock Animation. Sometimes animating icons in the dock can be useful in communicating the status of the system or application.