Though it does get a little funny, when you want to write org mode code blocks, that contain actually org mode code. If I recall correctly a "+" at the beginning of the line is then used for escaping?
I've not had time to explore fully, but I just cracked open emacs on this windwoes machine, and tried it, and it auto-added a comma to the beginning of a nested #+BEGIN_SRC...
blah
#+END_SRC
org-mode to the rescue ;p