Rails Scalability and Performance!
This is an interesting topic.
I am very interested in what is "state of the art" yet safe for production.
I just looked for Rails performance tuning books at Amazon.com
I found 1 which looks a little dated but probably still useful:
Enterprise Rails by Dan Chak
I looked over the table of contents.
It looks like Dan Chak likes to extract performance gains using caching and tuning the database (PostgreSQL).
I expanded my search to "websites" in general:
http://www.google.com/search?q=website+performance+tuning+books
Another thing which caught my eye is this:
From that URL I would be tempted to follow these lines of inquiry:
http://www.google.com/search?q=nginx http://www.google.com/search?q=gzip+compression http://www.google.com/search?q=varnish+http+cache http://www.google.com/search?q=routing+mesh http://www.google.com/search?q=load+balancer http://www.google.com/search?q=compiled+ruby http://www.google.com/search?q=ruby+vm http://www.google.com/search?q=thin+based+on+mongrel http://www.google.com/search?q=rack+middleware http://www.google.com/search?q=Rails+on+PostgreSQL http://www.google.com/search?q=PostgreSQL+Replication http://www.google.com/search?q=PostgreSQL+performance+tuning http://www.google.com/search?q=Memcached http://www.google.com/search?q=Routing+to+Memcached+instead+of+database
More obvious URLs:
http://www.google.com/search?q=rails+performance http://groups.google.com/group/rubyonrails-talk/search?q=performance+tuning&start=0&scoring=d& http://www.google.com/search?q=rails+performance+site%3Atwitter.com
Oh and then we have EY:
http://www.engineyard.com/technology http://www.engineyard.com/technology/ror http://www.engineyard.com/technology/webapps http://www.engineyard.com/technology/datastores