How important is the title of your book?

Let me say right from the start that the titles of my books are very important to me.  They often drive the narrative and sometimes they are a clue to some aspect of the plot. I don't pick them based on possible "market value" (even though I probably should) but instead they usually just materialize when I'm outlining the story arc.

My first book, Cyberdrome, was a combination of "cyber" (meaning man-machine interface) and "drome" (meaning arena) since my story took place inside a virtual world inhabited by digital avatars controlled either by humans or computer programs. It was essentially a meeting place for humans and A.I.

I consider it a coup d'état that I was able to snag the title "Novum" for my newest science fiction book (and eventual series) before any other SF author. Why? From the Oxford Dictionary of Science Fiction:

novum (n.) [Latin for "new"] the primary element in a work of science fiction by which the work is shown to exist in a different world than that of the reader. "...the term refers to those concrete innovations in lived history that awaken human collective consciousness out of a static present to awareness that history can be changed."

That describes my story so perfectly that I was actually panicked that someone else would publish something with that title before me, even though the term has been used in science fiction circles since the 70’s.

So how important is the title of your book, and how did you come up with it?