LinkedIn is a social website that is used to manage professional connections. Take for example the guy you worked with 3 years ago. Perhaps you're looking for a new job, and you remember he started his own company. Through LinkedIn you can find out if he has any job openings or perhaps one of his clients or friends does. Or, perhaps there's another colleague or former colleague that you though was just great to work with. You can write a recommendation for them on LinkedIn, to help them out the next time they're looking for new employment.
With LinkedIn's new RSS feature, you no longer have to login to the site to see what's new with your colleagues. Just add it to your RSS Reader, and you can view a headline of all their activity. Perhaps a current contact that you have in LinkedIn connects with a former colleague. Now that you see the former colleague has a LinkedIn account, you can send them a request to add them to your list of connections.
If you want to enable an RSS feed for yourself, go to the Accounts & Settings section -- the link is on the upper-right. Then scroll down to the bottom of the page, on the left side you will have an option to enable (or disable) your RSS feed and get the RSS feed URL.
Here is a link to my public LinkedIn profile. As of this post, I have 122 connections and 15 recommendations.