I you are used to doing forms in rails you probably used either start_form_tag or form_tag to open a form and end_form_tag to close it similar to this:

<%= form_tag :controller => 'users', :action => "search" %>
<%= text_field 'search', 'criteria' %>
<%= submit_tag 'Find a Friend' %>
<%= end_form_tag %>

This technique has been deprecated in Rails 1.2 and will be removed from the 2.0 release. Instead, you need to put the form inside of a block and pass it to the form_tag function like this:

<% form_tag(:controller => 'users', :action => "search") do %>
<%= text_field 'search', 'criteria' %>
<%= submit_tag 'Find a Friend' %>
<% end %>

Notice that we put the form inside of a block by adding do after the form_tag call and the end_form_tag was replaced by end and the <%= was changed to <% for the form_tag and end.

That should stop those annoying notices in your log and get you complient for the 2.0 release.