Show.html.haml
= fetch_partial "posts/post", :post => @post, :updated_at => (@post.updated_at rescue nil)

show action
  def show(id)
    @post = Post.get(id)
    raise NotFound unless @post
    display @post
  end

The tmp/ cache
tmp/fragments/home/justin/merb/blog/app/views/posts/_post.html--
_post.html--3df99173854b0158ad6ca14be4d7d44e31b75bf191437bded3f3e26046f5a792
_post.html--cedeaf1706c64425fc3cb61ba001ae1cdbfe83a500ad5af431cf519bb0f5a588

Every hit to the show action creates a new cache