I do.
Speaking of UIs, check out this badass motherfucker. I just finished setting it up on all of my characters. This UI comes equipped with Bartender (actionbars manager), Recount (DPS/damage monitor, also tracks other things like Healing per second), and Omen (detailed threat meter, shows who has the most aggro in your party for a given target). What's cool, though, is that these addons are actually implemented in the HUD itself, which you will see in these screenshots.
Mage - Here you can see the player frame (left), target frame (right), target of target (under target), Focus Target (under player), and Pet frame (under focus). The two bars on the bottom are your cast bar (bottom) and your target's cast bar (top). What isn't pictured (and I forgot to get a picture of it on my DK when my pet was the focus) is your focus target's cast bar, which shows up under the focus target frame to the left of the pet frame. You'll also notice the side-panels. You can attach a bartender hotbar to up to two side panels per side, but I only use one because two just won't fit unless I scale down my UI to unseeable proportions. I just made them Action Bar 3 (right) and Action Bar 4 (left) like the right bar and right bar 2 from the Blizzard UI. Also, the player, target, and pet frame portraits move, but you have to activate the portraits. By default they're just boring bars.
Death Knight - You'll notice that the UI has color presets for each class' color, as well as the ability to make your own color schemes and save them (you can also export them for others to add to their collection). Your target's buffs and debuffs appear above their portrait frame as well. The bottom two hotbars are your main bar (bottom) and action bar 2 (top). By default Bartender has shift-swapping (shift+bar number) disabled, but you can enable it for any bartender bar. I went ahead and enabled it for my main bar for convenience's sake. And
just above the action bars you can see a little meter. That's your "Swing Meter", AKA how long until your next auto attack. It can be useful for timing spells against your regular attacks, but other than that it's rather pointless (and fun). Something to note is that if I were fighting in a group, the in-game threat meter (the one that shows on your portrait, not Omen) would show up underneath these hotbars.
Warrior - More color schemes, yeah! Well, I've basically covered all the aspects of the HUD itself, so now I'll talk about how it works. If you'll look to the left, you'll see that the hotbar pane is closed. You can click the colored bar to open it up like the one on the right. The bar along the top shows different stats that are explained if you mouse over them, but they're rather self-explanatory. The main attractions are the buttons on the top middle and right. The four middle buttons (the colored ones above the orb) toggle your four panes along the bottom and flesh out the HUD. The left button is supposed to toggle the chat pane, I believe, but right now it only toggle the colored gradient background. The center left button toggles the Omen pane, which is on the left of the action bars. The center right button controls the Recount pane, which is on the right of the action bars. Finally, the right button toggles the Raid pane, which shows all the members of your raid for quick reference. The orb in the very center toggles all of these at once, favoring to turn everything on if you only have one or two panes on. Now, the buttons on the right, under the main frame, are your main menu buttons. Character, quest log, GM help, etc. The three buttons above that toggle other things. The big center one with the arrow pulls the menu bar up so you can hide it if you don't want it there. The small button on the right toggles the minimap, and the small button on the left open the "party and raid settings" window. You know, the one that has quick access to raid target markers, raid ground markers, readychecks, raid conversion, and all that good junk. In the normal Blizzard UI you would access it by clicking the arrow on the very left of your screen while in a party or raid.
This isn't how the UI looks at first. I've done some overhauling with the player/target frame positions as well as setting up Bartender. It's tedious and confusing at first, but once you figure out how it works you can set it up on one character, choose the "Default" profile, and then "copy settings from" that character's profile. Then all you have to do is on every subsequent character is "install" the UI (the first-time setup) and then "copy settings from" the Default profile, which you just loaded with your main settings. Then you can tweak it special for your character (you'll have to change the color scheme to your classes if you care, as that is included with the save to Default). I can .zip my setup and send it to anyone who wants to try it out, but otherwise check it out if you're bored with the default UI.
That said, there is only one major flaw. By default, the UI scales itself all the way to the smallest possible scale. For those with large resolutions, this makes the game nigh unreadable. However, it's easily fixed by going into System -> Advanced and then scaling the UI back up. Even so, you can only scale it up so far before the UI modules start to overlap and make it not look so good. The scale I took my screenshots at is two or three ticks above the scale it forces you at, and I found that was the perfect scale for my resolution. It's a bit smaller than I'm used to but I can deal with it, but if you can't then I would suggest not using this UI unless you don't want to use the Omen and Recount panes.
tl;dr - Cool customizable UI that looks a bit like the Starcraft 2 UI with only a few flaws.