High Scalability Building bigger, faster, more reliable websites.

Update 5: In Load Balancer Update Barry describes how WordPress.com moved from Pound to Nginx and are now "regularly serving about 8-9k requests/second and about 1.2Gbit/sec through a few Nginx instances and have plenty of room to grow!".
Update 4: Nginx better than Pound for load balancing. Pound spikes at 80% CPU, Nginx uses 3% and is easier to understand and better documented.
Update 3: igvita.com combines two cool tools together for better performance in Nginx and Memcached, a 400% boost!.
Update 2: Software Project on Installing Nginx Web Server w/ PHP and SSL. Breaking away from mother Apache can be a scary proposition and this kind of getting started article really helps easy the separation.
Update: Slicehost has some nice tutorials on setting up Nginx.

From their website:
Nginx ("engine x") is a high-performance HTTP server and reverse proxy, as well as an IMAP/POP3/SMTP proxy server. Nginx was written by Igor Sysoev for Rambler.ru, Russia's second-most visited website, where it has been running in production for over two and a half years. Igor has released the source code under a BSD-like license. Although still in beta, Nginx is known for its stability, rich feature set, simple configuration, and low resource consumption.

Update: Jake in Does Django really scale better than Rails? thinks apps like FFS shouldn't need so much hardware to scale.

In a short three months Friends for Sale (think Hot-or-Not with a market economy) grew to become a top 10 Facebook application handling 200 gorgeous requests per second and a stunning 300 million page views a month. They did all this using Ruby on Rails, two part time developers, a cluster of a dozen machines, and a fairly standard architecture. How did Friends for Sale scale to sell all those beautiful people? And how much do you think your friends are worth on the open market?

Shanti Braford details how his Ruby on Rails based website survived a 24 hour 550,000+ pageview digg attack. His post cleanly lays out all the juicy setup details, so there's not much I can add.

Hosting costs $370 a month for 1 web server, 1 database server, and sufficient bandwidth. The site is built on RoR, nginx, MySQL, and 7 mongrel servers. He thinks Rails 2.0 has improved performance and credits database avoidance and fragment caching for much of the performance boost.

Keep in mind his system is relatively static, but it's a very interesting and useful experience report.