God. Please stop with the "sexy". An application window or OS theme is not "sexy". What you mean to say is "visually appealing" or "cool" or "good".
For your education, here's a list of other things that are never sexy:
Cars
Lamps
Computer hardware
Computer software
Corporations
Industrial design
Cell phones
MP3 players
Packaging
That is all. Thank you.
Packaging could be sexy. What about Mrs. Butterworth's pancake syrup.