title: after_create :foo vs after_commit :bar, :on => :create
body: <p>Is there any difference between:</p>
  
  <p><code>after_create :after_create</code> and <code>after_commit :after_commit_on_create, :on =&gt; :create</code></p>
  
  <p>Can these be used interchangeably? </p>