I thought it might be useful for members running the Varnish content accelerator WHM plugin currently under development by UNIXy to have a thread where we can compare notes and exchange tips about using Varnish and the occasional tweak to a customer site to optimize the way it works with Varnish.
The two busiest domains on my main server are a world famous blog and a popular SMF discussion forum. On the day I installed Varnish the blog had just brought on new staff and merged in a Swedish site so the server load was higher than usual, running 2 to 3 in top.
I saw my load drop and the sites speed up literally the instant that Varnish was installed and running. Now my load average is just under 1 most of the time and the improvement in page load times is undeniable.