What are factors in the user experience that lead to users having an emotional tie to an interface, why, and what would be an example of each factor.
People build emotional ties to almost any interface that they have spent a lot of time using. Just take a look at people's reactions to almost any change of interface on Facebook or Gmail.
I don't think there are any design factors that make emotional links, like cute buttons or happy colours, though. It's simply about people having invested time into an interface and learn't to use it. When you change that, you are to an extent undoing some of their work, and therein lies the emotion.
People can identify with colors, fonts, shapes, just about anything. The industrial design of Apple products certainly is a classic example of design eliciting deep emotion and attachment, and the work of Dieter Rams preceded Apple by a few decades with the same appeal. On the software side, any well designed game provides instant examples of emotional and compelling interface design.
However, I would argue that interface elements are secondary to actual content and the user actions and tasks of an application in provoking emotional ties. For example, people are not attached to the simple blue button that says Like on Facebook. Rather, users are moved by what that Like button allows them to do - approve and ratify content, photos and links from their friends.
In short, allowing people to connect to basic human desires and psychological drives is what creates a compelling and loyal user experience. The interface is merely the medium.
Consistency and ease of use.
When users get so comfortable with your user interface that they can do their work with minimal thought about the tool and maximum thought about their task, they become dependent and attached to that interface. This can be good and bad. You may have established a strong connection to your user community and customers, however, it may be very hard to introduce a new (better in your eyes) interface because they are so attached to the old.
The simple answer is "Good UX". That means an interface that is highly intuitive, easy and straightforward to use, something people can use without thinking.
Th emotional bond is created, because applications are just useful and helpful. It is like I love my Virgin+ box, because it records stuff I want to watch, and I can do it without thinking. I love my phone (HTC Desire HD), because it is easy to use, and does all of the things I want it to. They both have good UX.
And the point from JohnGB is also important - that if a UX is good enough to draw people in, then people will learn the quirks and peculiarities. At that point, changing it is a negative experience.
Most people are uncomfortable with any device more complicated than a pencil sharpener. You may not hear spontaneous design feedback from these people because machines and user interfaces are not the most important things in their lives. Given a lack of choice, people will figure out a way to accomplish what they need using the tools they have even if they are not delighted by those tools.
It is easy to mistake a fear of change for an emotional bond. Gaining an adequate mastery of a device can be a painful process. Once achieved, mastery carries with it a degree of certainty; discarding the mastery evokes uncertainty and fear.
What user interface factors lead to an emotional bond? Ease of use and familiarity. Fear of new things, whether a new feature or a new device, is diminished when the new thing is like something they already know: if not the terrible, hard-to-use thing that they already mastered, then something else that is familiar to them.
I know we don't have to be talking about a website here, but in order to provide some context, that's what I'm going to assume below.
It's all about psychology.
People don't interact with a website and decide whether or not they are going to have an emotional attachment. Emotions are part of the subconscious, and therefore websites that wish to engage with the subconscious need to appeal in ways that the conscious mind is not even aware of.
The subconscious is processing massively more information than the conscious. It's looking for elements of danger, survival, food, sex. Some cues are going to appeal more than others - especially those that you can identify with or visualise easily.
A website that excites or arouses has a greater chance of being remembered and revisited.
Pictures engage the brain more than words, so pictures that appeal to your interests or desires will seem more attractive and be remembered even longer.
A website with beautiful pictures of luscious food is more appealing than wordy recipes.
A website that either demands or grows commitment from you in some form is in a small way building a relationship with you that means you are more likely to revisit.
If a website does you a little favour - whether it gives you no-strings-attached free shipping, or provides useful free information - is installing in you a sense of indebtedness which the subconscious will feel a need to repay by revisiting again.
We love stories - a website that tells a story is more engaging than one that just gives facts. Pictures and stories - a killer combo.
Websites that allow you to take part in social validation as part of a community or that enable you to feel good about yourself are very powerful at building emotional bonds.
If all this is combined with an appealing design and a great user experience, and you leave the website with a deep sense of satisfaction, then the bonds are surely formed. You'll tell people and you'll be sure to go back. You're smitten!
I thoroughly recommend Neuro Web Design by Susan Weinschenk about the psychology of designing persuasive and engaging websites by especially appealing to the subconscious. 5 minute into to the book. It's not a long book - you can read it in a few hours, but it tells a powerful story - with pictures and most of the above ideas were examined in this book.