this is what I have in my view:

<%  form_remote_tag :url => { :controller => 'comments', :action => "create", :post_id => "#{@post.id}"}, :html => {:id => 'comment_form' },
      :before => "tinyMCE.triggerSave(true,true);" do %>

    <%=  label_tag 'Comment' %><br/>
    <%= text_area_tag :comment_body, nil,:rows => 10, :cols => 100 %><br/>

   <p style="margin-top: 10px;">
      <%= submit_tag 'Add',:id => 'btnCommentSave' %>
    </p>
  <% end %>

Tinymce editor is displayed properly.

In my controller: how to get the contents of the text area? I am expecting the contents in params[:comment_body] and I am not seeing it?

I tried doing this also,

 $('#btnCommentSave').click( function(){
    tinyMCE.triggerSave(true,true);
    $('#comment_form').submit();
});

What am I missing? Thanks