gistfile1.txt

application.html.erb:

<%= generate_menu_link do %> <%= link_to "Home", :controller => "pages", :action => "show" %> <% end %>

application_helper.erb:

  def generate_menu_link(&block)
    link = with_output_buffer(&block)
    li = ""
    if is_link_to_current_page?(link)
      li = '<li id="link-to-current-page">'
    else
      li = '<li>'
    end
    
    output = li + link + '</li>'
    output.html_safe
  end
  
  def is_link_to_current_page? (link)
    @current_url ||= request.fullpath
    @current_url == link
    link_url = link.match(/\bhref="[^"]*/)[0].gsub('href="','')
    @current_url == link_url
  end

Result if we're linking to the current page:

<li id="link-to-current-page"><a href="#">#</a></li>

Result if we're not:

<li><a href="#">#</a></li>