I posted a story over on Open Source Catholic today concerning page caching and its importance for saving a server under a heavy load (read: the slashdot effect). You can save a lot of resources on your server by not only using built-in page caching on your favorite CMS, but also exploring further options (for Drupal, there's Boost (read our case study on Boost); for WordPress, there's WP Super Cache). From OSC:
A couple months ago, the Archdiocese of Saint Louis announced that a new Archbishop had been chosen (then-Archbishop-elect Robert J. Carlson). For the announcement, the Archdiocese streamed the press conference online, then posted pictures on the St. Louis Review website of the day's events (updated every hour or two).
During this period of time, the Archdiocesan website had over 2,000 visitors per hour, and almost all the visitors were hitting the home page. The website (run on Joomla 1.0.x) didn't have many caching mechanisms in place, and for almost a complete hour, the website was returning server errors as the processor was pegged at 100% utilization. Something had to be done!