There is a real issue here. This past week, I've shut the type cover on my surface, went to the bed, and the next morning the battery icon showed that the batter charge had fallen by 25-30%.
Something is wrong... I will point out that I never had this issue on 8.1 Preview.
Well, I did a very unscientific, but very real-life oriented, test last evening. I found that based on my average use pattern, the RT gives me about 8 hours of use (actually, I could only stay awake till the 7 hour mark, but noted that I had around 23 or 25% of battery left, which would have easily given me the one additional hour). Now, about shutting the cover and the RT going to sleep or whatever it is that it is supposed to do to maintain the connected standby profile, I am not sure how that works out. Have not consciously looked for it.
But I would not be surprised if there is a problem - but nothing that a firmware update from MS can't fix. I'll look out for this issue on my Surface 2 (which is, as of now, only a couple of hours old).