Using your images in an applications is usually very easy. When you use a TIFF or PDF image, your image will automatically be drawn at the correct resolution, making it easy to adopt resolution independence.
One thing to remember if you are using your image for a button or an image in a status menu is the NSImage template property. By setting an image to be a template (using the [image setTemplate:YES] method), you tell the system to do smart image processing of the image to make it look great. This works best with grayscale images.
You can also export your image as Source Code to generate code that will dynamically redraw your image's contents. Cocoa, Cocoa Touch, Core Animation, and Quartz code are great for applications for the Mac and iOS.