what do you use to indicate book titles and/or quotations?

Roman.

Italics originated as standalone designs, only later have we started to use them for emphasis within a family (roman, italic, bold ++).

what do you use to indicate book titles and/or quotations?

Qoutation marks?

I think what you guys are saying is true on a historical level, but you have to know you are really moving against the grain if you are using italics for large portions of body text. Many studies indicate that readability has to do with training, so for instance even though sans-serifs have a slightly easier definable shape, most people still find serif-fonts faster to read in large quanta. It's like with music and a lot of other things - you don't have to follow all the defined rules, but you have to know that you achieve a certain effect if you break them. If you set body text in italic, you probably will get a certain reaction (either conscious or subconscious) in the readers.

Of course you will use roman to indicate book titles - as you do in for instance image captions where italic is the "normal" text.

I have to agree with hassebasse, typographic conventions are established regardless of where they historically originated.

Personally I use the Economist book of style to sort out arguments (you don't have to go by it, but it helps to have a guide, why constantly re-invent the wheel?). When working with an experienced editor, I'm always willing to debate, but in the end these things can be an editorial decision.

I've just recently been dealing with a case where italics are used, I believe, inappropriately ( on our road signs here in Ireland). One of my arguments against this (beyond the legibility concerns!) is that conventionally italics are used to indicate a foreign language phrase, so using it for our native language demeans it in relation to English.

Like any rule, it just requires a full and thoughtful understanding, before you set about breaking it.

Garrett Reil
http://raindesign.com
http://garrettreil.ie

Italics originated as standalone designs, only later ...

Just a reminder: lowercase letters originated as standalone designs, and we are long accustomed to using them together with caps. :-)

Andreas

"you are really moving against the grain if you are using italics for large portions of body text."

Going against the grain isn't inherently a bad thing! Forbidden is nothing. Make decisions with care, and think about what they imply/cause.
For instance, from what I understand, italics tend to slow down reading speed. And then of course, they tend to have a different flavor than the Roman, hence giving the text a different tone. Do you want these things? Do you need them? Observe carefully.

Also: This whole question depends a lot on the design of the Italic at hand. That's one reason why I personally favor somewhat "subdued"/subtly differentiated italics with structures closer to slanted-romans – they're easier to use for stretches of text too if you need that; and when they're well-designed, they work just as well for emphasis. A classically chiro-"swirly" Italic on the other hand, which diverges a lot structurally from its Roman, is a lot less flexible as a companion.

FWIW, I just designed/typeset a book where one chapter consists of interview-like question/answer paragraphs. The editor insisted on having the questions in italics – and sometimes those are half a page in length. At first I groaned; but choosing the right font fixed it, and it works pretty well now in terms of marking a rather subtle difference in tone.* But I'd say don't do this with a classical Garalde face.

(* Not a difference in color – I offset that by choosing a slightly heavier weight. Beware that many Italics will be lighter than their Romans, and might be too light for extended text.)