I love this post over at Hots and Dots, and it almost makes me wish I'd done the same thing with my UI (though truthfully, I don't get too complicated, so most of my pictures would look like her first one). Lathere has collected a series of screenshots of her UI, showing off how much its changed over the years, from her first raids in Karazhan up to the current raids in VoA and Ulduar. And it's very cool to see how things have changed -- early on, she really adhered to addons and what they did as a default, and as time passes, you can see that not only are the addons getting better at giving you the tools to lay out the UI the way you want it (not to mention that other tech has gotten better as well -- she goes widescreen about halfway through), but she's getting better at customizing things exactly the way they should be. The UI gets much more abstract and simplistic as time goes on, though you'd presume that it actually lets her do more in terms of her character.
In fact, aside from the actual graphics in the background and the icons, it's almost hard to tell this is the same game. Of course, Blizzard has to keep a lot of things in the default UI the same, so they leave a lot of the really creative edits in the UI to the addon developers (and then, of course, steal the most interesting back). And they can get very creative indeed -- when you put these screenshots over a period of years up against each other, it's interesting to see how both the addon code and the player has changed the interface they use to play the game.