RSS feeds are a way to find out when news or information is updated on a website without going to that site. PSD is experimenting with these feeds as a way to keep users informed of dataset updates and changes.
To use, either open the URL in a browser that can handle RSS (IE 7, Firefox, Safari) or open a News aggreator like NetNews. Subscribe to the feed for news readers or bookmark it for browsers. Different programs handle RSS feeds in different ways so experiement with several to find one with the features you like.
More info on RSS can be found at Wikipedia or you can do a web search.