Can you provide us with an idea of how much this improved performance or how many more requests it allowed you to handle? Were there time or cost savings compared to alternative approaches?
For us our main goal is to prevent the majority of requests from even reaching the Rails stack. We've done this by introducing full page caching across the site, for both logged in and logged out users. This means that only a small percentage of requests at peak times need to touch Rails or any database at all - everything is served by Nginx.
This hasn't been without its challenges. The last section of this post might give a clue as to how we've solved the most difficult ones. I will think about a post tackling this whole subject but I need to think about how to get it across, it's not easy.
It is a very fast module, and non-blocking, but just as importantly it provides the flexibility to avoid sending requests from Nginx to slow backend servers (Ruby, Python, whatever) at all. In real-life situations, this is the most important bit.
As I said in another thread, we've done some good work to tie this in with our Rails app. We now page cache almost every important request, even for logged in users. This means Rails and our databases are protected from most spikes of traffic. I would like to write a post describing this in more detail, I need to think how to get it across though.