We all want beautiful things. A beautiful graphic user interface is no exception. But how do you define beauty? Pretty colors? Balanced composition? Elegant typography? Appealing trimmings? Grid fidelity?
Without diminishing those things, my feeling is that, when it comes to GUIs, the most beautiful are the ones you don't notice. The beautiful GUI is so useful, so understandable, so usable that you don't even think about the inteface — you're totally absorbed in what you're doing via the interface. This is true for simple devices as well as for complex expert apps where, once you get familiar with the tools, you just use them without thinking.
Expert interfaces are for experts
The thing about expert interfaces is that, while they are complex, they are optimized so that a well-trained user can use them efficiently. For example, non-linear video editing systems like Avid Media Composer are rather complex. They have lots of tools that bring great power to the editor. They also have keyboard shortcuts for nearly every function, and ready buttons for commonly needed items. Once the user is practiced on the system, the expert interface becomes much easier to use than the simple interface. For example, a professional video editor would go nuts trying to work in iMovie — it's just too simple!
And yet for the casual user, iMovie is much more useful, much more usable, much more transparent. In other words, the complexity of the interface depends upon the knowledge, experience and needs of the user.
This is perhaps one reason why Apple has gotten so much flack for reinventing the UI, among other things, of FInal Cut Pro. Expert interfaces require hours of training and practice. Apple has ripped many tools out, changed much of the rest, and added yet new things. For the casual video editor, Final Cut Pro X may be like manna from heaven, but for video editing professionals it requires retraining, and the missing features may render such training not worth the investment. Meanwhile, if you have to think about how you're doing instead of what you're doing, you're simply not as productive.
The same would be true for a feature-rich community site. Change how everything works and you'll have a riot from the community members. The features don't belong to the website, they belong to the users. "What happened to my sort button?" Suddenly they have to focus on the interface, not on what they are doing with it.
The unnoticed interface
What is the best user interface? I would argue that one example is a very low-tech object: eyeglasses. They are devices that are a means to an end — seeing. If they are dirty — that is, if you notice them — then they suck. All of us who wear glasses probably share the experience at one time or another of searching for the glasses that we were wearing at the time. (One time recently I was tearing the house apart. My glasses are for nearsightedness mostly; I can't see up close with them on. When I went to the couch to see if they got tucked into the cushions, I took off my glasses to see better— *facepalm*.)
Other user interfaces we don't notice: doorknobs, the driving controls on our cars, water faucets, dresser drawers. All of these, except for the automobile controls, are simple, and the automobile controls are dependent upon some standardization and all of us sharing some basic training on their use. If a manufacturer came out with a new car that put steering in the pedals and throttle on a lever, never mind what governments would do, the buyers would stay away — their driving training would be of little use.
On websites, most of which cater by necessity to the casual user — even regular visitors don't want to invest hours of training just to be able to post a comment — we're seeing much standardization in functionality, layout, even icons usage. Is this bad? Is this boring? Is this bad design? Or is it making these sites more usable, more transparent so users can focus on what they're doing, be it reading, posting, linking, uploading, liking, tweeting...? And isn't that what we want? Sites that make it easy for users to do the things they (and we) want them to do?
What is a website but a means to an end? If the user is noticing the website, instead of doing what she needs to do, then it's quite possible that the website is non-optimal. Its UI lens is dirty.