Ever since the Panda update from Google, a lot of attention has been given to duplicate content.
In a recent video from Matt Cutts of Google, he answers the question of whether or not using a quote from another source is considered duplicate content. The answer is no, if it is not used to extreme.
Quoting other reliable sources is a good way to adding value to your articles or blog posts. It is important to keep the quote short, and not use a lot of quotes in a given article. It is also encouraged to give the source of your quote, as well as a link to the source.
Here is Matt Cutt’s video explanation of the question: