So I've been wasting time by searching for titles on the Nano site. I mean, I'm not searching for a title for my work, but what people have come up with their own work. Fortunately, no one has taken my tentative title yet (which is tangentially related to lobster physiology).
Unfortunately (for other people, that is) there have been inadvertent duplication of titles. Just search for a common word like "dream" and it's all too obvious. I don't think anyone's going to get prosecuted for having the same titles--there are already books in existence that have the same titles, easily provable by searching on Amazon.com--but to me, it'll just be that more difficult for one's work to get exposure because it can be confused with someone else's work.