It started on Friday 9/26. I hadn't updated to 8.0.2 yet but I was getting messages from my provided telling me that my data was nearing it's limit. First at 65%, then to 90% within the next hour. I reset my cellular usage statistic and quickly found out that it's the Mail app. It's using ~10MB per minute. No explanation. I'm not sure if it's a bug with the app itself, or a bug with the mail protocol between Google and the iPhone. This entire experience has been extremely frustrating. Has anybody else been experiencing this, or anything similar?