I have just created a thread on my specific problem, but might be helpful to this one too.
To all of you having these drain issues... check when the case is closed that the keyboard is not still illuminated.
This is happening to me, and draining faster than it should - I noticed that the keyboard backlight was basically permanently on when the case was closed....
So, when you open the case, is the keyboard illuminated straight away even before you have had a chance to wake and unlock the iPad? Mine is - and that tells you its been permanently illuminated since you last closed it.
Wondering if this is software related, or faulty hardware.