We use metaphors all the time. I suspect it's hard to imagine quite how often we use them, since most metaphors don't take the obvious form of, "She is the angel of my heart." (Though of course they can.)
Actually, a lot of the fantastic, active, interesting verbs we're encouraged to use rely on metaphor for their meanings. "He barreled down the hall" uses a metaphor. So does "The cats like to rocket around the house." So does, "The dog shot out of the barn and over the wall."
Then of course there are the larger metaphors. A hilarious example of this is George Carlin's famous routine about the differences between baseball and football. Baseball is a game, and football is a war - at least metaphorically. There can be no better testimony to the power of metaphors to inspire strong feeling than to watch Carlin make faces as he makes the comparison. The way we speak about things influences the way we react to them.
Now, George Carlin is a very funny man, but part of the power of that routine is that metaphors do strongly influence how we think about life. When negotiations are described using war metaphors, the participants are more likely to believe that only one side can win - when in many cases, there is an optimal solution that will help both sides. Politicians choose their words carefully (and even use focus groups!) in order to make use of the feelings that metaphors can inspire in us.
This is one reason why I encourage people who are working with alien or fantasy worlds to think about the metaphors that their characters use to understand their lives. My favorite example (as blog readers will no doubt know) is my character Rulii who thought of life in terms of hunting, and therefore called colleagues "huntmates" and his goals "quarry."
Today I'd like to go one step further in considering metaphor, and look at three places in science fiction and fantasy writing where metaphors can play a critical role.
First is magic. When you're designing a magic system, watch out for the metaphors that crop up. If you're trying to create a highly organized, rule-based system, you'll probably want to identify a single metaphor that can help you to handle your descriptions of magic use. Some books treat magic as if it were water; some treat it like wind. Others treat it like bullets shot out of a wand that stands in for a gun. My own novel, Through This Gate, had ink magic. The choice of this underlying metaphor will give you a sense of how the magic can be controlled and how it behaves; also, how it might be countered or broken. Consistency of metaphor is often crucial. If you've got your magic acting like gravity in one place and like bullets in another, people will notice - and they may object. It can be worth taking a special pass through a manuscript to check the kinds of adjectives and verbs used to describe magic, and making sure that they are all consistent with a single underlying metaphorical concept.
Second is technology. How many of us are actively conscious of our association of technology with "progress"? What if technology were not assigned that metaphorical value, but an entirely different one (like art, perhaps)? I'm sure you are all familiar with the portrayal of virtual space as one "above" reality, or "inside" a computer. This, too, is a metaphorical choice, which puts the virtual space in a position like that of heaven, or in the second case in the position of the inside of a dollhouse or gameboard. I'm sure you can think of other possibilities. The story I'm currently editing, "Mind Locker," uses an entirely different metaphor, one associated with the new concept of augmented reality, where the virtual "overlays" reality, in a sense reversing the idea of a heavenly/platonically ideal space into one that invades the earthly plane.
Last for today is "issues." Whenever you are dealing with important and conflict-filled issues like gender, racial, ethnic, or language identity, pay close attention to the metaphors that you are using. The feelings that they provoke will infuse emotion and judgment into your portrayal of these critical issues, and if you aren't paying attention, you may end up provoking something you hadn't intended. For one thing, you want to make sure that if you're working in a secondary world, the metaphors you associate with personal identity characteristics are appropriate to the world you are working in, and not to ours. Allowing metaphorical associations to creep in from our world can change the feeling of a created world drastically, and can sometimes become confusing. For example, do the people of your world think of race in terms of coloration, or some other criterion? Is the most useful metaphor one of "blood" and the dilution of blood, or something else? Switching to gender now, are females "flowers" in your world? Might men be "cats"? Why? When I was designing my Varin world, I had to be very careful with how I used metaphorical descriptions. Skin color there varies, but is not a critical identity criterion in the way that caste is, because though the initial population had different skin tones, there has been no immigration for a thousand years and interbreeding has been constant. Once you factor in that everyone has lived underground that whole time, you end up with a group that varies between "golden" and "pale," with the exception of the few people who actually do spend time on the surface (and they vary from freckled to brown-skinned). I therefore tried to dissociate the metaphors usually used with skin tone, and reassign them for use with caste identities, so that "blood" refers to the quality of one's caste.
There is so much more I could say here, but I will leave you with this: metaphors are everywhere, and they have powerful links directly into your emotions. It's worth taking the time to analyze them consciously and make sure that, as a writer, you are using them to their full potential.
It's something to think about.