Which words don't get capitalized in the title of a book?

And, or, of, with, to.

John Gruber explained what he does for his Daring Fireball blog titles.

There’s no official rule; it’s whatever the author / publisher decides. The first word, no matter what it is, will usually be capitalized. Articles and prepositions are usually lowercase if not the first word, and pronouns tend to be capitalized.

Wikipedia says both lower case and lowercase are correct (and also minuscule).

What Pete said, above.

Chicago Manual of Style, my constant companion when writing:
http://www.amazon.com/Chicago-Manual-Style-University-Press/dp/0226104036/

Here’s a good example; Love in the Time of Cholera.

if e.e. cummings wrote it probably none of the letters.

or
[may
be] 1
randomLy [cap
it al] ized
l e t t e r

e.e. cummings should not be degraded in such a manner!

I’m sorry, I wasn’t thinking. You’re right. I apologize.

Modern Language Association (MLA) says articles (a, an, the), conjunctions and prepositions are not capitalized. The MLA format cover most Humanities publications and films. The APA and Chicago Manual of Style follow different conventions.

This is a matter of style, and style guides do vary. Some style guides specify that prepositions of 4 or more letters get capped, and some say 5 or more letters. Articles and conjunctions are normally lowercase. But the first word of a title always gets capped, no matter what it is (and it is often “the”). Typically the last word does too. Also a preposition is usually capped when it is part of a phrasal verb (for example, “show up”). All verbs are always capped.

In the example cited, “we” and “it” are pronouns. All nouns and all pronouns would be capped. The part of speech is the first determiner, and not the length of the word. Any book publisher will have a house style that they follow; but for a specific book, variant typography may also be used for some marketing purpose.