Some useful bundler commands in Rails 3.

gem install bundler #installs bundler
bundle install #reads gem list from Gemfile and installs them
bundle check #check gem list from Gemfile and sees if any aren't installed yet
bundle help #lists available commands
bundle install --without=test #like install but ignores test env gems
bundle lock #freezes gems to current versions
bundle install --relock #unlock gems, update and lock again
bundle pack #installs gems locally to vendor/cache