There are three new useful resources up for those of you who are working with KML (or thinking about working with KML!)
First, there we've added a page to the KML documentation on Google Search for KML Files and GeoRSS Feeds. This guide takes you through the basic ways to make your geo content discoverable by Google, so that it will show up in searches in Google Maps or Google Earth as user-generated content. In particular, it discusses the inclusion of the ATOM elements
link in KML documents for attribution. You might also want to check out the Developer Day presentation by Pamela Fox and Lior Rion on geo Search and using KML and GeoRSS in the Maps API.
As Pamela mentioned in that presentation, I recently posted an article on Using PHP and MySQL to create KML. This tutorial walks you through creating a MySQL database table, populating it with data, using PHP (4 or 5) to transform it into KML, and overlaying it on a map. This is a useful tutorial if you are storing data in a database and want to show it in Maps or Google Earth, or even just output it for indexing by Google.