While watching different idéas for the GUI-design I often think "That's beautiful, but is it functional?". My opinion is that the GUI should be functional /usable and beautiful. Are there any special effects they should have a function of usability.

Transparency in the terminal windows: Do you have to know where the trash is when using the terminal?
Aqua dock imitations or Dockbert variations: They look very nice, but are they really usable? You don't even see the name of the window (the icon represent) unless you hold the pointer over it. The classic BeOS dock is very good to use. Windows are grouped by application, and you don't see more than you need to.

There are many more examples on good and bad GUI designs.

I recommend all GUI designers to read a book by Donald Norman, for example "The Design of Everyday Things". You will get more comprehension of what's usable and not usable.
I can also recommend this webpage about GUI-design, guuui.com [1].