bill - 5:46 am on Feb 28, 2013 (gmt 0)
I implemented DMARC on several domains last year. It's interesting to see reports on mail that can't be tracked as coming from my servers. There's not much, but it does exist.
I hope more big companies implement this. It's simple to setup, and you can run it in reporting mode until you're ready to move to the stricter settings.