mac osxにmemcachedをインストール。

$ sudo port install memcached
Password:
--->  Fetching libevent
--->  Attempting to fetch libevent-1.4.3-stable.tar.gz from http://monkey.org/~provos/
--->  Verifying checksum(s) for libevent
--->  Extracting libevent
--->  Configuring libevent
--->  Building libevent with target all
--->  Staging libevent into destroot
--->  Installing libevent 1.4.3_0
--->  Activating libevent 1.4.3_0
--->  Cleaning libevent
--->  Fetching memcached
--->  Attempting to fetch memcached-1.2.5.tar.gz from http://www.danga.com/memcached/dist/
--->  Verifying checksum(s) for memcached
--->  Extracting memcached
--->  Configuring memcached
--->  Building memcached with target all
--->  Staging memcached into destroot
--->  Creating launchd control script
###########################################################
# A startup item has been generated that will aid in
# starting memcached with launchd. It is disabled
# by default. Execute the following command to start it,
# and to cause it to launch at startup:
#
# sudo launchctl load -w /Library/LaunchDaemons/org.macports.memcached.plist
###########################################################
--->  Installing memcached 1.2.5_2
--->  Activating memcached 1.2.5_2
--->  Cleaning memcached

memcachedの自動起動を設定。

$ sudo launchctl load -w /Library/LaunchDaemons/org.macports.memcached.plist

cached_modelをインストール。(memcache-clientもインストールされる。)

$ sudo gem install cached_model

config/environment.rb

require 'memcache'
memcache_options = {
  :c_threshold => 10_000,
  :compression => true,
  :debug => false,
  :namespace => ":app-#{RAILS_ENV}",
  :readonly => false,
  :urlencode => false
}
CACHE = MemCache.new memcache_options
CACHE.servers = 'localhost:11211'
ActionController::Base.session_options[:expires] = 1800
ActionController::Base.session_options[:cache] = CACHE

参考:
memcached Basics for Rails | Ruby on Rails for Newbies
memcached: a distributed memory object caching system
memcached公式サイト
Installing memcached | Development, Analysis And Research
memcahcedのインストール方法
Rails fragment cache with memcached-client and time-based :expire option - skwpspace
railsのfragment cacheでmemcachedを使うためのプラグイン
railsのセッション管理でmemcachedを利用 - dreammindの日記
FFTT : memcached
[memcached] memcached導入手順 - Life with IT