According to Shyam WordPress.com which serves 4 million plus page views per day is moving its frontend serving needs to Nginx.
Automattic to be consistent with their brand want an all opensource stack.
Nginx is super fast, reliable, and stable. You can squeeze a lot more juice out of a server with Nginx than you can with Apache. Using Nginx is almost like having two servers running Apache – except, faster, more reliable and stable.
According to Quantcast, WordPress.com’s network traffic including its subdomains, and hosted domains make it the 6th most visited site.
A quick analysis shows WordPress.com using Nginx 0.6.29.
