Quotes can be copyright protected and/or registered trademarks. Copyright violations are punishable by a fine of up to $150,000.
Check the two web sites below for more information.
Giving credit to the author is a "fair use" thing that applies to commentary and criticism only. You can use a quote from a book if you're posting a book review on a blog because you're not profiting from it. You can't put a quote from a book on a t-shirt or coffee mug and sell it.
Copyright expires at some point, however; generally 70 to 120 years from the time the artist or author dies. So if you're quoting from a book that's over 150 to 200 years old that is most likely not a copyright violation. You'll still need to check and make sure the quote is not a registered trademark.
