"however I never did understand this"
Usually, it was the people from Windows 2000 hating XP - its interface was a bit too "toy-like" for those used to a simpler one, and some elements (i.e. the windows title bars) took really too much space, especially on smaller displays like laptops. Many returned to the older interface.
I eventually settled on the "Zune" theme, which, despite its name, was a nice black/orange theme with simpler bars and smaller windows icons, and a better overall look.