Using simple_form with twitter bootstrap 3.0. These are the changes I made when upgrading.

simple_form_bootstrap_3.rb

SimpleForm.setup do |config|
  config.wrappers :bootstrap, :tag => 'div', :class => 'form-group', :error_class => 'error' do |b|
    b.use :html5
    b.use :placeholder
    b.use :label
    b.wrapper :tag => 'div', :class=> 'col-lg-10' do |ba|
      ba.use :input # , :class => ['form-control']
      ba.use :error, :wrap_with => { :tag => 'span', :class => 'help-inline' }
      ba.use :hint,  :wrap_with => { :tag => 'p', :class => 'help-block' }
    end
  end

  config.default_wrapper = :bootstrap

  config.label_class = 'control-label col-lg-2'

end

# In each simple_form_for call
defaults: { input_html: { class: "form-control" } }