Looks Like AWS Billing has surprises like your cell phone bill, billing alerts added

Ken Oestrich has a tweet on AWS's new billing alerts.

Heh. Got AWS Billing Alerts notice today. IMO acknowledging "Umm... you may be using more AWS than you or your org realizes" + / - ?

 AWS posts on the new feature.

Monitor Estimated Charges Using Billing Alerts

Because the AWS Cloud operates on a pay-as-you-go model, your monthly bill will reflect your actual usage. In situations where your overall consumption can vary from hour to hour, it is always a good idea to log in to the AWS portal and check your account activity on a regular basis. We want to make this process easier and simpler because we know that you have more important things to do.

To this end, you can now monitor your estimated AWS using our new billing alerts, which Amazon CloudWatch metrics and alarms.

AWS is a driven by customer requests.  Like Ken says there is a good chance that users are getting hit by higher AWS bills than they anticipated.
The beauty of the Cloud is it scales, but with that scale comes a higher bill.