as Rabbi Rachel says, "genderless sovereignty." From an occult point of view, the idea of malkuth as "the kingdom" is used more as the idea of being the Earth itself, or the grounding, the bringing of energy into physical manifestation. This isn't so far off from the basic idea presented over on The Velveteen Rabbi's blog.
I see malkuth as being the sephirot of manifestation, yes. It is the place where my prayers, visualizations, dreams, and hopes become real. Remember that saying, "be careful what you wish for; you may get it"? That's a part of malkuth, too. This is the place where Spirit (by whatever name you call the god or portion of god who touches you in the real world) makes dreams real. I have to be careful what I think of, what I wish for, because Spirit may choose to manifest them for me.
This, to me, applies in so many ways. In going through the crumbling of my current relationship, I have found myself thinking several uncharitable thoughts about the people who went from "family" to "barely tolerated housemates." Sometimes, I give in to those thoughts, noticing them and revelling in them for a short while. Other times, I am a better person, taking a step back and asking how I would feel if others thought of ME that way.
My very thoughts, the words I speak, are all things of power. If I don't want to manifest negative things in my life, I have to be watchful that I don't invoke those negative things in my words, actions, or even thoughts. This isn't to say I have to be perfect - everyone breaks down sometimes and things, "Gee, what an ass!" The point is to catch yourself and stop the thought. "Not an ass. Just unpleasant to me. I can walk away from this; it is not my problem."
So much anger and frustration could be dissipated easily, if we could just take that step back.