nginx seems to be popular at wordpress

here is why : it's an very fast load balancer and is easy to use

nginx gains more than a million sites; more than doubling in numbers. The WordPress blogging system recently converted all of its load balancers to nginx, using the upstream hash module to serve 8-9 thousand requests per second. Netcraft's site report shows the main WordPress site switching from LiteSpeed to nginx in April. nginx is a web server and mail proxy server written by Igor Sysoev.