To avoid duplicate form submissions, Rails has a nice option for submit tags:
submit_tag "Submit", :disable_with => "Saving..."
This adds behavior to the submit button to disable it once clicked, and to display "Saving..." instead of "Submit".
Rails 4+
DEPRECATION WARNING: :disable_with option is deprecated and
will be removed from Rails 4.1. Use 'data: { disable_with: 'Text' }' instead.
Thus the above becomes:
submit_tag 'Submit', data: { disable_with: 'Text' }