In 2009 we evaluated the use of f5 Web Accelator caching technology for our website. We didn't end up using the product but it was pretty educational for me. We have a high number of pages that would not be cached due to cookie values and certain business rules our company had the led to the page requests not being able to be cached.

While much of our images, css, and javascript files would be cached, a large percentage of our web pages were not. Since the page loads were what was causing the high CPU Utilization on the webservers the f5 Web Accelerator wasn't saving us a lot of that time.