Just recently purchased my Ipad... for the past two mornings when I went to turn on my I-page, which was charged the evening before, the battery was completely dead. Am I not turning off a correct on/off switch? the one at the top right of the I-Pad viewing it vertical?
Your iPad should not be draining completely over night. I have had odd things like this happen on my iPod Touch if the cable was not seated completely in the docking port on the bottom of the iPod. Instead of charging the device, it ended up draining the battery!
I haven't had this happen with my iPad... yet! I would say that if it keeps happening, it might be time to take your iPad to an Apple store or at least call Apple Care and ask them.
What were you doing before you pressed the Sleep button for the night? Do you have Location Services turned On or maybe left an app running all night? Sometimes if there is a constant refresh, some apps will still run all night long even though you put it to sleep. (At least that's what occasionally happens to my iPhone).
And are you turning it off or merely putting it to Sleep? You use the same button to do either. Sleep = one press of the buttton. Off = press and hold that button until you see the "Slide to power off" slider. You have to slide that to the right if you want to actually turn it off.
Figured out that I was not powering it off.. I'm learning
The first few days I had my iPad, I didn't even know there WAS an on-off button, lol. 1991-C4 kindly pointed me to the user guide, which is extremely useful.
So far, I haven't had a problem like yours. The iPad should go to sleep after ~5 minutes even if you don't use the on-off button. I have GPS tracking etc constantly on, and there doesn't seem to be any parasitic drain of the type you are experiencing.
Have you installed a program/app that keeps eating power even when the iPad is off?