What is the meaning of life?

Meaning is not an inherent property of the universe. Meaning is a construct on the part of some conscious mind (see themusic's writup on meaning--"Meaning doesn't mean anything; only people mean"). Specifically, the meaning of some thing (idea/person/place/whatever) to a given conscious mind is an isomorphism (association, if you like) between it and (some portion of) the mind's representation of reality.

There is a human tendency to deny this idea that meaning is not inherent--i.e., to project the meaning we hold internally as an inherent property of its object.
Why do we do this? Well, here's my best guess: Humans are naturally insecure of their own mortality and thus (usually) very protective of their lives. The idea that meaning is just as mortal as we are makes us insecure of and so weakens our internal model for the world. Thus, to understand the world in practice, we believe (or pretend to believe, though there isn't much difference) in our meanings as persisting throughout the world they describe rather than only in our heads. However, in theory, it is possible to understand that meaning is indeed not inherent. That is, we may "believe" that meaning is not inherent and at the same time "believe" in our meanings.

So, what's the meaning of life then? The meaning of (my) life, (my) existence, is my life, my existence. That sounds like the typical kind of "deep thoughts" copout that can be produced almost mechanically, but it isn't: the meaning of any thing is the isomorphism between it and one's internal representation of reality. The isomorphism between my existence/life/universe and my representation of it must be (I claim) the identity mapping. Thus, my answer above seems meaningless (heh, heh) because that's as much meaning as you can get out of that question.

To me, the question is simply the wrong one. To ask for an inherent meaning in life is to give up its inherent freedom. I ask instead, "What should I do with my life/today/right now?" and "What part do I play in what goes on around me (especially society)?", among others.

When I have less time, though, I still answer "42". To me, Adams captured the essence with that answer, i.e., Mu - unask the question, it's the wrong one.

Afterthought: In some sense, society has a mind of its own, and each individual in it is conscious of it to some degree. This provides some insight into how we perceive meaning as something objective, as we see that other people tend to agree with our meanings--see collective subjectivism.