There really isn't any policy on this. Just note that content is [licensed under cc-by-sa][1], but Stack Exchange additionally requires you to:

> (…) attribute the work in the manner specified by the author or licensor (…)

So if you quote (or copy without using visual indication of a quote) content from a Stack Exchange site, you should at the very least include a link. But that's all there is to it, really.

The idea of generating reputation from content that the author has not originally posted does not seem to go well with the current model, where reputation is a *direct* measure of a person's involvement on the site the reputation was gained on.* If you quote someone's post and link to it, and the reader has an account on the source site, they can upvote the original content if they want.

<sub>* except the association bonus</sub>

  [1]: http://creativecommons.org/licenses/by-sa/2.5/