Simple ruby module to make rolling out features easy...

features.rb

module Features
  def self.allowed?(feature, user)
    case redis.get(key(feature))
    when "admin": user.admin
    when "diy": user.admin || user.diy
    when "enterprise": user.admin || !user.diy
    when "all": true
    when /^\d+$/: user.admin || user.id % state.to_i == 0
    else
      false
    end
  end
  
  def self.rollout(feature, user, &block)
    yield if allowed?(feature, user)
  end
  
  #Dirty dirty magic...
  class << self
    [:admin, :diy, :enterprise, :all].each do |state|
      define_method(state.to_s+"!") do |feature|
        redis.set(key(feature), state)
      end
    end
  end
  
  def self.percentage!(feature, percentage)
    raise "percentage must be between 0 & 100" unless (0..100).include?(percentage.to_i)
    redis.set(key(feature), percentage.to_i)
  end
  
  def self.disable!(feature)
    redis.del(key(feature))
  end
  
  def self.redis
    $redis
  end
  
  def self.key(feature)
    "feature:#{feature}"
  end
  
  module Helpers
    def allowed?(feature)
      Features.allowed?(feature, session[:user])
    end
    
    def rollout(feature, &block)
      Features.rollout(feature, session[:user], &block)
    end
  end
end

Once we are totally comfortable with the feature we remove the rollout lines.

It'd be great to avoid too frequent roundtrips to redis. You can have a redis-configurable TTL for this class. It'll be totally fine to hit redis once every minute or five. If it's configurable, you can crank it down to be 1 second if you want to really play with the feature.

Can we make it more nuclear? If you disable JobHistory, Rollout can patch JobHistory so that all methods return a FeatureDisabled object. This way you avoid littering your code with conditional statements. (thinking aloud)

I'm sure various e-mail senders will use rollout very quickly :)

hrmm. +1 pimp.