PHP 5's ability to read XML files is fantastically easy to use. In the past it was possible but it required quite a bit of long winded code to get any where. PHP 5's SimpleXmlElement function makes working with XML a breeze, and with much less code too!
They include a script as an example - five lines to completely parse and pull the title and link information out of the remote RSS file. The example creates a SimpleXML object using the feed's URL and makes each element inside accessible as an object (that can be looped through and properties can be checked on).