Are the things I read about Kundhalini and whatnot metaphorical or do people generally mean them in a literal sense?
I've always wondered about this phenomenon.

I assure you that kundalini practitioners, on average, are not speaking in metaphor. However, its hard to answer your question to a larger degree than that as it is so vague. Can you be more specific?

what things? like siddhis and bliss absorption, waking lucid dream states and the transmission of shaktipat and all that stuff?

those are spoken about literally. Someone who has fully awakened their kundalini is working with a different energy in themselves than someone who hasn't. in some powerful people its like a raging bonfire as opposed to a candle. Some people can really handle a lot of energy, and do amazing things thereby.

a person can be lost in kundalini powers and not have awareness or wakedness in the buddhist sense, so some schools make a big deal about kundalini like its the goal itself, and some schools, like buddhists in general, take a neti neti approach where its just a stage on the path, another thing to let go of basically.

it does bring interesting insights and awakening with it though.

hope that answers your question, i agree its pretty vague so maybe being more specific would help

There are a couple of distinctions to be made here which may help clarify your understanding: first of all, there are the descriptions of the physiological sensations common to what are termed "kundalini" experiences - e.g. sensations of warmth surging up the spine, "sexual" sensations emanating from the base of the spine and the genitals, physical shaking, and so on - which, in my experience, are literal [1] and can be repeated by anyone interest in pursuing the relevant practices; secondly, there are the descriptions of the mental, emotional and/or psychological aspects of the experience - a sense of expanding to become infinite space, feeling as if you become one with "God", visions of archetypal figures, precognitive experiences - which, in my experience, can only be described metaphorically [2] since their literal explanation would require considerable medical study and research.

In the words of Korzybski: "The map is not the territory it describes" - This is something useful to keep in mind.

Hope that helps.

[1] Literal: "in accordance with, involving, or being the primary or strict meaning of the word or words; not figurative or metaphorical: the literal meaning of a word." - [Link]
[2] Metaphor: "something used, or regarded as being used, to represent something else; emblem; symbol." - [Link]