With the update to Formtastic version 2.0.0.rc1 the ‘semantic_remote_form_for’ method was removed and support was added to ‘remote_form_for’ used like this:

<%= semantic_form_for @contact, :remote => true, :url => '/contact' do |f| %>

This is to conform with the new Rails 3 update where form_remote_for is replaced with form_for with a remote hash value passed to it as an argument.