Alright, my second shot at writing a little about RSS. The previous attempt resulted in "The Church of XML":http://www.zefhemel.com/archives/2004/09/12/the-church-of-xml. I'll briefly describe what RSS is and why it is useful. I won't talk about the internals of the RSS XML format, simply because they're too boring. RSS stands for Really Simple Syndication. It is an XML format that is used to publish changes of something, anything. Today it's most used for news websites and weblogs, but it can just as easily be used to publish the latest commits to CVS or changes to college timetables. A couple of years ago many sites already published such a feed, but most of the time they used their own custom format, which made you make a new parser for every feed. Those feeds were mainly meant to include other site's news into your own. Some people considered (and still consider) it cool to have the latest "Slashdot":http://www.slashdot.org headlines on their website.
Today however there are standardized formats for this type of syndication, the most well known being RSS 0.9x, RSS 2.0 and Atom. RSS 0.9x are versions based on the standard originally developed by Netscape, RSS 2.0 is a slight improvement on that old format. Atom is a newly designed format which is said to include all the old RSS format features and everything that was missing, whatever that may be. "A better description of RSS can be found here.":http://www.xml.com/pub/a/2002/12/18/dive-into-xml.html
If your site doesn't have some kind of RSS feed today it can't be considered cool. All cool websites have RSS feeds today, even worse, uncool websites have them too. The really cool ones have more than one, such as mine (check the left menu, under feeds).
The trouble with those RSS feeds is that they're XML files, which normal people don't like reading. That's why RSS feed aggregators were invented. These applications let you subscribe to as many feeds as you like, regularily check those feeds for updates and show them in a nice GUI. There are many aggregators today, I used "SharpReader":http://www.sharpreader.com for a while, which is a .NET framework client application. The trouble with it was that it ate half of my memory. Today I use "BlogLines":http://www.bloglines.com, a web-based aggregator. It does exactly what it has to, and also offers the opportunity to have a public version of your subscriptions, "here's mine, for example":http://www.bloglines.com/public/zefhemel. Bloglines also allows to export your subscriptions to an OPML file, which is a standard XML format to store feed subscriptions (most aggregators can import and export this format). I also noticed "Thunderbird":http://www.mozilla.org/products/thunderbird/, my e-mail application of choice, has a built-in feed aggregator (starting at version 0.8, currently the latest version):
Will RSS replace the regular web? No. RSS is a convenient way to keep up with updates of hundreds of sites that change a lot. For many weblogs it's an alternative way of reading, though. Many weblogs publish the full content in their feeds. There are weblogs that I never visited through a webbrowser, only through its RSS feed. Some XML APIs and aggregators even make it possible to comment using the aggregator, eliminating any reason to visit the website. This makes it very hard to measure how many people are actually reading your weblog. You could see how many hits your RSS feed is getting, but that's only an indication of how many subscribers you have (and how often they check), not how many actually read your stuff.
I would highly encourage everyone to pick an aggregator and start subscribing to feeds. It really helps you to keep up with the latest developments in all the areas you're interested in. If you don't know to what feeds to subscribe, have a look at "mine":http://www.bloglines.com/public/zefhemel for some starting points. There's also a search engine for RSS feeds, called "Feedster":http://www.feedster.com. Feedster indexes thousands of RSS feeds and allows to quickly search through all of them.