A humanized interface is one that feels more like a helpful and kind human than a lifeless, cold computer program. Good software is like as a good personal assistant: it doesn't get in your way; it anticipates your needs; it does what you mean, not what you say; and it pays attention to details you may have overlooked.
On his blog, photographer Brad Moore describes what makes a great assistant to a photographer. And although the article is not talking about computers at all, it's exactly what you want from good software. Read this as if it were a manifesto for the personality of your software, and imagine replacing each instance of "the photographer" with "the user."
In my opinion, three things… Attitude, anticipation, and attention
If you have a great attitude, that will go a long way… it makes each
day easier to get through and gives them one less thing to stress
Being able to anticipate the photographer's next move is also key.
Knowing how they think through not just a shoot, but through problems
that arise will allow you to have something ready without them needing
Attention to detail… When assistants learn the photographer’s shooting style,
likes, and dislikes, they can help keep an eye on how things are
going. With the photographer’s mind (and eye) being on multiple
things at once, there are sometimes things that they don’t notice that
an assistant can pick up on and point out (in a discreet,
non-distracting manner, especially if the client is on the shoot as
Obviously knowledge of the gear is important too, but I think these
are probably some of the most important but most overlooked things
that help make a good assistant.
Notice how at the end the article says that the technical knowledge needs to be there too, but that the human attributes (attitude, anticipation, and attention to detail) are more important and are often overlooked. The same is true for software. We often spend so much time getting the technical details right while overlooking the most important attributes: what we can do to give our software a human touch.
Have some personality
Just like with your personal relationships, you want to interact with software that has a pleasant personality. You have to decide which personality is most appropriate for your application, but most people like to interact with people that are warm and friendly, maybe even light-hearted.
Do what I mean, not what I say
Good software will try to read between the lines. It tries to interpret what you intend, which may be different from what you say. It will make reasonable assumptions based on what it has learned about you, and it keeps a memory or your interactions so you don't have to repeat yourself.
One example: when you mistype something into Google like [hmuanised interfaces], it guesses at what you meant, just like a helpful human would do. It doesn't throw an error, it doesn't show zero results, it doesn't imply that you're stupid, and it doesn't draw any more attention to your mistake than necessary. It kindly says that it's "Showing results for humanised interfaces" because it interpreted what you meant, not what you said.
Keep track of the details
A good assistant will keep an eye out for details you might forget so you can focus on the big picture. It will check for errors for you, fixing them when appropriate or just telling you about it otherwise.