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I almost always use absolute URLs. Dana has a point about efficiency, and a lot of developers HATE writing anything but relative URLs, but I think most modern servers can handle the load just fine, and developers can be bribed with cookies. The advantage of Absolute URLs is they're less likely to break with various CMS's (content management systems) and on-page elements. I've seen javascript do some crazy things to relative URLs causing 1000's of broken, uncrawlable links. And when your content is scraped, either for black hat reasons or perfectly legitimate reasons like embedded RSS feeds, then you get full credit for the link. But to be fair, and to recognize Gamer07's point, Google likely devalues most of these links anyway once they detect the duplicate content.