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Dan Collis-Puro has a great article on how Harvard Law used Nginx as a front-end proxy for WordPress, and has released a WordPress plugin which outputs some HTTP headers to interface with Nginx, also available in the article. The readme has information on how to get things set up.
Here's the article:
Note that at Harvard Law, they've completely abandoned all WP-side caching in favor of Nginx. The additional complexity in the WP side, they found, was completely unnecessary after getting nginx set up.