To the OP: Run your battery all the way down until the device shuts off, then recharge overnight until it's full. I think you'll see FAR better performance.
I bought my 3G at the beginning of the week. Came out of the box with 80% charge. Used it a while and it seemed to drain down to 40% too fast. Charged it to 100% overnight, and the next day it again seemed to drain too fast. But once I FULLY drained the battery (took a couple days of periodic use without charging), THEN recharged to 100%, the rate of battery drainage dropped way down. I haven't done a formal test but it feels like the 10 hrs quoted.
So, when you first buy the iPad, the meter and charging system may be off calibration. Only a full discharge and recharge will fix it. Give it a try.
In general you should do this once every 1-2 months on any rechargeable device.
I recall reading somewhere that Apple recommends that you totally drain your battery the first 2 or 3 times and recharge fully each time to get the best battery function. I just can't find a link to the article anywhere.