ML is Mountain Lion the newest Mac OS. It is going to be available for download at some point today via the Mac App Store. Since you have purchased a new Mac, you get ML for free instead of having to pay 19.99 (US) for it.
You will need to fill in the form on this page to get ML:
http://www.apple.com/osx/uptodate/
I believe you need to fill in your new MBP's serial number on the Up To Date webpage in order to confirm you are eligible to get ML for free so the email I received today is important as it contains the serial number.
My order was placed on July 2nd and was originally scheduled for delivery between Aug. 6th-10th but now has a more precise Aug. 2nd date. From the exp.o website, it looks like they are requesting a delivery date of July 27th which is either the date it will start it's final delivery to my place OR is when it is expected to arrive at my place. At this point, I still have no tracking info from Apple itself or even a courier. Nada.
Check your original delivery notification email from Apple and look for a delivery number starting with '8' and put that number in the box under Track Your Freight and then press Search. Don't change anything else. It should then give you tracking info like I showed a few posts ago.