form_remote_tag not displaying button

Clem,

Your code needs to look like this:

<%= form_remote_tag :url => { :action => :add_to_cart, :id => product }
do %>
  <%= submit_tag "Add to Cart" %>
<%= end_form_tag %>

The <% ... %> tags will evaluate the code between them without
outputting the result into the HTML. The <%= ... %> tags, on the other
hand, will output the result.

Hope that helps,
Matt Buck