In the children's section of the store, we have a book called Zero is the Leaves on the Tree. It helps explain the concept of zero to kids.
But my geek-side is starting to bug me about this. In the case of the book's title, zero is a concept, which is why the verb "to be" is singular. But if I were talking about the number itself, I would say, "There are zero leaves on the tree." Zero is a plural, despite being nothing at all.
I've been having a hard time coming up with a reliable source that gives a definitive answer to this. There are several websites that talk about the history of the number - I found it interesting that the word "zero" came from the Italian word for wind (zefiro), which was close to the Arabic word for zero (sifr).
The best I can tell is this: zero is a plural because you can often have a lot of it. For example, "There are zero leaves on the tree." Zero, in that sentence, refers to the lack of leaves. And there used to be a lot of leaves. There is a complete lack of them.
After a bit more searching, I've found something here.
2. zero - having no measurable or otherwise determinable value; "the goal is zero population growth" no - quantifier; used with either mass nouns or plural count nouns for indicating a complete or almost complete lack or zero quantity of; "we have no bananas"; "no eggs left and no money to buy any"; "have you no decency?"; "did it with no help"; "I'll get you there in no time"
Which is to say what I said above.