Study found that only 12% of all users are aware of RSS, and just 4% had knowingly used the technology for reading feeds from blogs, news sources and other regularly updated content sources on the web. If you're unfamiliar with RSS, click this link for a textual explanation or this one for a funny but superb video explanation (recommended).

Because webmasters are more aware of what RSS-feeds can offer, it is more used to have fresh changing content automatically on your site from all the interesting sources you find on the web. Different forms of presentation are possible. To keep a fast performance of your site, the feeds are cached on your server and refreshed after a certain period.

Besides the little widgets visible on this page, you can also have a more serious RSS-aggregator to integrate feeds in the theme of your site. Here you can even delete single items inside a feed (some you want, others not).

Some examples of RSS-feed tickers (mouse over = pause):