I often tell people, as I've learned, that the first rule in design is to "never design without a concept" and the second rule is to "never design for the sake of design." These two rules are very important and go hand-in-hand.
What this means is that you can't just go right away and dive into a design without thinking about it (whether that means sketches, wireframes, comps, or whatever gets you understanding what you're doing); and never let that concept only mean that it looks pretty. The latter means to never let your concept "be" simply because it works from a compositional sense.
Of course if you're a designer that usually means you're also an artist. We know that. But where design has to definitely be aesthetically pleasing, it also has to be part of what you're designing for. That's not to say that your designs need to have the perceived purpose.
Now Use a Horse's Head
I know I beat the Horse's Head concept into the ground as a tool for getting designers/developers to stop worrying and try using new technologies in web development. Now I'm saying that you should also look at using it as inspiration for getting your users to stop worrying and use your site. It's the other side of what I've been saying.
The horse's head worked because it gave the industry's users piece-of-mind that they weren't going to hell for driving an automobile... well... it at least encouraged them by giving them the perception that it was as easy as driving the carriages they were use to. Here's what I'm talking about:
Piece of Mind Design is Everywhere
Take for instance the "Door Close" button on an elevator. I read somewhere that it actually does nothing. I think a fireman might push it with another button in order to force the elevator to do something magical. But either way, it might as well just be a button that does nothing. You still have to wait if you push it by itself... the same amount of time as if you didn't push it.
The fan in a bathroom is arguably ineffective. I think if you keep your bathroom pretty cold, it might have some effect because warm air rises, but, if you notice, you still gag when you need to go to the bathroom, if you happen to work in an office with a bunch of developers (just saying.) You might think that if you leave the fan on for awhile it actually does something... but it doesn't. In fact, I'm convinced that the only real purpose it serves is helping you cancel out any grunts, duck calls, sinking golf balls, snoring, or whatever other sounds that might be in happening in there. (Psst. That doesn't actually work all that well, either, unless it's an older fan... and if you're that guy that sleeps in the bathroom at work, you really need some allergy medication.) I actually don't think anyone really wants to admit any of that... sorry.
In case you were a "LOST" fan, Desmond was told that he needed to enter a sequence into a computer and then push execute every two 108 minutes to 'save the world'... and he did it for years and never missed a beat so that he could have piece-of-mind. (I hated the ending BTW... such a cop-out.)
I'm sure you can keep going with that.
A Live Example
I recently had a project where someone might need to place a large order of items based on store inventory. The the user would save this order in the app. The developer was all about nixing the save button that I had in my mockups and having it auto-save. I really liked that idea of auto-saving but I knew that it was going to freak people out, so I suggested that we have at least a "saving..." — "all changes saved" text that promptly appears at the top of what the user was doing... kinda like Google Docs.
Well... it was shown to the decision-makers before that was in place and sure-enough they had a hard time believing that it was saved. It was better received when he placed the saving text in, but they started suggesting Save/Edit modes, which would have caused the whole feature to be rewritten. So, what we came up with was a "Save" button... that does nothing... except for pop-up and highlight the saved text.
When you have a cool technology that you're excited about getting a chance to use, it can be hard to support the user. Your audience is the thing that needs to be thought of first so that they are in the back of your mind through the whole design process. Dave has a great piece on personas that can help you understand who's using your app.
I'd also like to hear more examples of piece-of-mind design. Please share.