I really want to create a stunning-looking GUI desktop application that looks like, for example:
I think that the major reason many people suck at designing interfaces is that they consider them to be graphic design. It is not. The core of creating a good user interface is a bit like creating a good API – the interface has to be conceptually consistent, hard to misuse, easy for common tasks.
Wanting to design something cool because you are “tired of plain GUI” is a perfect recipe for disaster. If for nothing else then because consistency is a crucial part of a good UI. If each application wanted to stay out of the crowd, the whole thing would be an unusable mess.
It is almost unfortunate that Mac OS X looks that good, because then people start to think you can create a good interface by animating it or sprinkling some graphics on the top of it. The graphical part, the “cool” of the design is just the icing on the cake. If you really want to design good interfaces, stay true to the environment, respect local human interface guidelines. And maybe read Apple’s Human Interface Guidelines to get a feeling where the problems are and what can be done to solve them.
I know this sounds much more boring than filling gradients in Photoshop, but it’s the only right approach to take if you really want to create a top-notch interface.