My latest project's Gemfile, implements bundle group pattern

Gemfile

##### See Gemfile.md for detailed notes on specific gems #####
source 'https://rubygems.org'

# Gemfile.mine in root dir allows locally custom gems.
# NOTE: Doing this will change the Gemfile.lock - commit with care.
eval File.read(File.join(File.dirname(__FILE__), 'Gemfile.mine')) if File.exists? File.join(File.dirname(__FILE__), 'Gemfile.mine')

ruby '1.9.3'

#################### Rails 3.2 ####################
# NOTE on branching:  We are using the rails 4 track gems as much as possible,
#                     because in most cases they retain support for Rails 3,
#                     and there will fewer issues with upgrading to Rails 4 when the time comes.
gem 'rails', '~> 3.2.11'
gem 'simple_form', '~> 2.0.4'
gem 'dismissible_helpers'
group :assets do
  gem 'sprockets-rails', '~> 0.0.1'
  gem 'sass-rails', '~> 3.2.5'
  gem 'coffee-rails', '~> 3.2.2'
end
#################### /Rails 3.2 ####################

#################### Rails 4.0 ####################
#gem 'rails',     github: 'rails/rails'
#gem 'journey',   github: 'rails/journey'
#gem 'arel',      github: 'rails/arel'
#gem 'activerecord-deprecated_finders', github: 'rails/activerecord-deprecated_finders'
#gem 'activerecord-session_store', github: 'rails/activerecord-session_store'
#group :assets do
#  gem 'sprockets-rails', github: 'rails/sprockets-rails'
#  gem 'sass-rails',   github: 'rails/sass-rails'
#  gem 'coffee-rails', github: 'rails/coffee-rails'
#end
#gem 'simple_form', github: 'plataformatec/simple_form', branch: 'rails_4'

# TODO: These are deprecated functionality of Rails 3 removed from Rails4
#       We will use this to transition, but ultimately change our code to not rely on it
#gem 'protected_attributes', github: 'rails/protected_attributes'
#################### /Rails 4.0 ####################

# The Webserver
gem 'puma', '~> 2.0.0.b4' # 1.6.3 has issues with NewRelic
# The Database
gem 'pg'
# More power to the Database
gem 'pg_power', '~> 1.3.0' #, github: 'acquaintable/pg_power', branch: 'rails4'
# Allows PostgreSQLto use the new HSTORE from Rails 4
gem 'activerecord-postgres-hstore', '0.5.2'
# The Cache - Redis can back Object Caches, I18n, Session, HTTP Cache
gem 'redis', '~> 3.0.2'
gem 'redis-namespace', '~> 1.2.1'
gem 'redis-rails'
gem 'redis-store'
# View Template Language
gem 'slim', '~> 1.3.5'
gem 'slim-rails', '~> 1.1.0'
# Assets stored on AWS S3
gem 'aws-sdk', '~> 1.8.0'
gem 'asset_sync', '~> 0.5.0'
# Allows rack to rewrite requests, no need for Apache mod_rewrite
gem 'rack-rewrite'
# Neo4j REST API
gem 'neography', '1.0.3'
# Voting On Things
gem 'thumbs_up', '~> 0.6.2'
# Versioning Things and Soft-Deletes
gem 'vestal_versions'
# To avoid indecent exposure of instance variables in the view
gem 'decent_exposure'
# Base for JSON
gem 'json', '~> 1.7.6'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 0.9.1'
# Fast JSON Object parsing and marshalling
gem 'oj'
# Implant jQuery directly into the Asset Pipeline ========>
gem 'jquery-rails', '~> 2.1.4'
# Markdown Parser (for copy)
gem 'redcarpet'
# Our Queue
gem 'sidekiq'
gem 'sidekiq-failures'
# Queue Manager
gem 'hirefire-resource', '~> 0.0.2'
# Third Party Email Service
gem 'sendgrid', '>= 1.0.1'
# Registration, Authentication, Invitation, Confirmation
gem 'devise', github: 'idl3/devise', branch: 'rails4'
gem 'devise_invitable', github: 'sunny36/devise_invitable', :ref => '5af50a925e0a41cc648b124ffe7de0f8f081481e'
gem 'devise-async'
# Facebook Oauth
gem 'koala', '~> 1.6.0'
gem 'omniauth', '~> 1.1.1'
gem 'omniauth-facebook', '~> 1.4.1'
# Authorization
gem 'cancan', '>= 1.6.8'
gem 'rolify', '>= 3.2.0'
# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks', '~> 0.6.1'
# Errors
gem 'exception_notification', '~> 3.0.0', require: 'exception_notifier'
gem 'exceptional', '~> 2.0.33'
# Code Metrics
gem 'newrelic_rpm', '~> 3.5.5.540.dev'
# User Metrics
gem 'km', '~> 1.1.3'
gem 'analytical'
# But User Metrics from the client-side!
gem 'event_tracker', github: 'acquaintable/event_tracker'
# Geolocations
gem 'geokit', '~> 1.6.5'
gem 'geokit-rails3', github: 'acquaintable/geokit-rails3'
# Mobile Response
gem 'mobylette', '~> 3.3.2'
# Mobile Push
gem 'urbanairship', '~> 2.2.0'
# App, Service & Environment Config
gem 'figaro', github: 'acquaintable/figaro', branch: 'rails4'
# Stateful Behavior
gem 'state_machine', '~> 1.1.2'
# Find bad queries
gem 'bullet', '~> 4.3.0'
# Mini Controllers & tiny mounted Rack apps inside Rails for widgety things
gem 'cells', '~> 3.8.6'#, :path => '/Users/pboling/Documents/src/other/cells' #:git => 'git://github.com/acquaintable/cells.git'
# A/B Testing
gem 'split', '~> 0.4.6'
# XML Parsing
gem 'nokogiri', '~> 1.5.6'
# Abstraction Layer over the WebSocket protocol
gem 'websocket', '~> 1.0.6'
# Yet another framework
gem 'sinatra', :require => nil
# The rails app administration tool
gem 'rails_admin'
# AJAX file upload
gem 'remotipart'
# Automated Sitemap and SEO
gem 'sitemap_generator'
# HTML5 Boilerplate
gem 'html5-rails'
# Possessive form of a string
gem 'possessive'
# To use dummy images built on-demand for rapid prototyping
# Depends on an install of imagemagick and the rmagick gem
# TODO:Verify Setup instructions for ImageMagick before uncommenting rmagick
#gem 'rmagick'
#gem 'dummy_image', :git => 'git://github.com/davelyon/dummy_image.git'

#################### Peter Boling's gems ####################
# Debugging toolbar, heir of rack-bug
gem 'rack-insight'
# Add messages to your flash messaging stack whenever you need to, array-style
gem 'stackable_flash'
# Use the cookie for transporting the flash messages and javascript to render them into the view
gem 'cacheable_flash'
# Map any methods on any Ruby objects to a CSV export, and vice verse.
gem 'csv_pirate', '~> 5.0.7'
# Redirect all email in non-Production environments to alternate, safe, addresses
gem 'sanitize_email', '~> 1.0.5'
# Bit fields for Active Record - Follows conventions of standard boolean columns.
gem 'flag_shih_tzu', '~> 0.3.2'
# Views can be and should be 100% DRY
gem 'dry_views', '~> 0.0.2'
#################### /Peter Boling's gems ####################

# Gems used only for assets and not required
# in production environments by default.
group :assets do
  gem 'uglifier', '>= 1.3.0'
  gem 'handlebars_assets', '~> 0.8.1'
  gem 'compass-rails', github: 'ai/compass-rails', branch: 'rails4' #'>= 1.0.3'
  gem 'compass-h5bp'
  gem 'zurb-foundation', '>= 3.2.3'
  gem 'foundation-icons-sass-rails', '~> 2.0.0'
end

group :development do
  gem 'quiet_assets', github: 'evrone/quiet_assets'
  gem 'better_errors', '>= 0.3.2'
  gem 'annotate', '>=2.5.0'

  # Allows us to magically convert directories of haml templates to slim templates
  gem 'haml2slim', '>= 0.4.6'
  gem 'haml', '>= 3.1.7'
  gem 'haml-rails', '>= 0.3.5'
  # Check for Security Holes
  gem 'brakeman'
end

group :development, :test do
  gem 'powder', '~> 0.1.8'
  gem 'rails_best_practices', '~> 1.13.2'
  #gem 'ruby-prof', '~> 0.11.3', require: false
  gem 'rspec-rails', '>= 2.12'
  gem 'fabrication', '>= 2.5.2'
  gem 'parallel_tests', '~> 0.9.2'
  gem 'teabag', github: 'acquaintable/teabag'
  gem 'pry', '~> 0.9.10'
  gem 'pry-rails'
  gem 'pry-doc'
  gem 'pry-remote'
  # Guard
  gem 'guard'
  gem 'guard-spork'
  gem 'guard-rspec', '~> 2.3.3'
  gem 'rb-inotify', :require => false
  gem 'rb-fsevent', :require => false
  gem 'wdm', :platforms => [:mswin, :mingw], :require => false
  # Mac OS X Notification center
  gem 'terminal-notifier-guard'
  # Spork
  gem 'spork-rails'
end

group :test do
  gem 'remarkable_activerecord', '>=4.0.0.alpha2'
  gem 'cane', '~> 2.5.0'
  gem 'test-unit', '~> 2.5.3'
  gem 'mocha', '0.13.1', require: false
  #gem 'rspec-apotomo', :git => 'git://github.com/kristianmandrup/rspec-apotomo.git', :ref => '03a2ac2f526fa668ee3a4bdb09cbc41693931ca3'
  gem 'rspec-cells', github: 'acquaintable/rspec-cells'
  gem 'shoulda-matchers', github: 'acquaintable/shoulda-matchers'
  gem 'bourne', github: 'thoughtbot/bourne'
  gem 'capybara', '>= 2.0.2'
  gem 'capybara-email'
  gem 'poltergeist', github: 'brutuscat/poltergeist'
  gem 'vcr', '~> 2.3.0'
  gem 'fakeweb', '~> 1.3.0'
  gem 'autotest', '4.4.6'
  gem 'autotest-rails', '4.1.2'
  gem 'simplecov', '~> 0.7.1', require: false
  gem 'database_cleaner', '>= 0.9.1'
  gem 'email_spec', '>= 1.4.0'
end