wpmuorg have published an in depth article “WordPress Multisite with Nginx – How to set it all up and enjoy the blazing fast consequences” written by by Gwyneth Llewelyn.
“Recently, due to the many attacks launched on the internet, especially the botnet DDoS attacking WordPress hosts, I was forced to move some of my sites to a shared server — a virtual machine — with little memory and just a slice of one CPU core.
This required rethinking the whole strategy of hosting them: instead of having huge server with almost unlimited memory, disk space, many CPU cores, and infinite resources, I had to somehow extract the same amount of performance out of this tiny virtual server. How?”
Read full article: http://wpmu.org/wordpress-multisite-wordpress-nginx/