We use the autoblog plugin to curate articles from our network of bloggers. We want to do as much as possible to ensure that they are not penalized by Google, especially in light of the recent Panda update. Google has said that it will look for the rel="canonical" tag to indicate that a link is pointing to the original source. Right now, there is a checkbox for adding rel="nofollow" but not canonical. We've hacked the plugin to include it on our site, but would love to see it added to the next release.