On the SitePoint PHP blog today there's a new tutorial showing how to use the SimplePie aggregation library to create a "lifestream" website of all of your accounts across the web.
In this tutorial we'll build a page that gathers up the RSS feeds of all those little bits of your life and presents them all together in one spot. To do that, we'll use SimplePie, a feed parsing class written in PHP. It's powerful, it's open source, and it's easy to use. We'll then hack on the output a little, and make it all look gorgeous with HTML and CSS. The techniques we'll cover are also useful if you find that you need to aggregate RSS from many sources, like a news page.
In their example they pull together accounts from Twitter, Flickr and Last.fm. You can check out the code for their example script here.