Thanks. It took 42 days from interview to "In line for oath" email..
Yes I sent them by mail. It took me ~45 days to get my oath letter.
Several factors: The DO is rather small; my case was really open-and-shut to begin with (just a minor clarification that also came up during the GC process); I requested an InfoPass on 07/02/13, the oath letter says my case was approved 07/03/13. I really think it's the bureaucracy of red tape that's holding things back.
Be patient! I'm sure it will come through