Hi, all,
Just finished here (Using Nginx, SSI and Memcache to Make Your Web Applications Faster :: Oleksiy Kovyrin and-memcache-to-make-your-web-applications-faster/) my detailed description of how we cache rails sites in our project - this idea allows me to handle hundreds of queries with one server running pretty slow (yeah! it is slow even after all optimizations on MySQL side and lots of tweaks in site's code) Ruby on Rails application.
Thanks, Alexey Kovyrin