I love my Ubuntu greatly, and most of what I do on it is theming -- I change my wallpaper every time I login, and more often than not I change my whole theme!
So today I decided to expand my GUI customization -- I installed xubuntu-desktop. And I must say, it's quite refreshing to learn how to use something new, and to see what works best for me.
The ability for Linux to be so customizable is one of the reasons for its success, and it couldn't happen without the open-source model. It's great to have these two pillars of desktop environments (GNOME and KDE), each of which "compete" with each other, not for profit, but to make the GUI better. And the smaller GUIs also benefit from this competition.
A closed-source, monopolistic system like Microsoft's could never offer this kind of customization. Yes, it's possible to hack your way into a new look for WinXP, but it's just not something that Microsoft supports or makes easier. And when there's only one desktop environment (and a broken one at that) in Windows, what incentive is there to innovate and make it better?
It's interesting that one of the most decorative features of an OS has shown me the advantages of the open-source system.
So, a hearty thank-you to Linux, (x/k/?)ubuntu, and the open-source model!
And one question -- what other good desktop environments are there, and how can I install them in Ubuntu?