Resolution Independence
The old assumption that displays are 72dpi has been rendered obsolete by advances in display technology. Macs now ship with displays that sport native resolutions of 100dpi or better. Furthermore, the number of pixels per inch will continue to increase dramatically over the next few years. This will make displays crisper and smoother, but it also means that interfaces that are pixel-based will shrink to the point of being unusable. The solution is to remove the 72dpi assumption that has been the norm. In Leopard, the system, including the Carbon and Cocoa frameworks, will be able to draw user interface elements using a scale factor. This will let the user interface maintain the same physical size while gaining resolution and crispness from high dpi displays.
The introduction of resolution independence may mean that there is work that you’ll need to do in order to make your application look as good as possible. For modern Cocoa and Carbon applications, most of the work will center around raster-based resources. For older applications that use QuickDraw, more work will be required to replace QuickDraw-based calls with Quartz ones.