I haven't used any more data then usual. Our billing cycle closed the other day and my line had used the same amount I have always used. So far this cycle I have used a minuscule amount of data since I am on WiFi at home and at work I don't use my phone...so if it is a bug it looks like it isn't effecting everyone.
I been waitiing to add my response to this thread. At first it looked as if my usage stayed normal, so I decided to wait at least a week before checking my usage.
According to AT&T I used 640mb half way through plan for the month. This would have put me around 1.2gb which is average for me. In just a week I used 900mb already with iPhone 5. Ouch. I have another week before plan renews. I guess I'm gla I still have unlimited. This pone is starting to make me rethink the idea to move to a data share plan so I can get tethering and FaceTime. It's a little more than double from my iPhone 4.