In my position as webmaster of Share Our Strength, I am constantly on the lookout for better and easier methods of generating content to drive visitors to our many websites. One exceedingly easy method is to grab content from outside RSS feeds, allowing a page on our site to have constantly updating content from another site. Working with RSS is so easy that when I'm in a rush, I sometimes grab our own content through RSS, just to save time.
Grabbing rss content to post on your own page is perfectly permissible, both legally and ethically. Firstly, because when you grab a feed, you are not only linking to them, but also driving visitors to their site, but, more importantly, because by publishing an rss feed, they are inviting users to use that content. (People can even monetize their feeds by using Google Adsense for Feeds.)
But what if you find regularly updated content that doesn't use a feed?
Feedity is a service that creates an rss feed from a regularly updated page that does not utilize an rss feed. This means you could grab another site's content automatically without their consent.
[EDIT: Entry never finished, but I'm publishing as is anyway, in case it helps others flesh out this concept.]