It's come to our attention that our subscription processor had an issue that caused many customers to get double charged for their subscription today. We're still looking into the extent of the issue and will update each impacted store.
In the meantime, if you had subscriptions that ran today and your store version was 072, you may want to void the duplicate transactions via your payment gateway and contact the customers to let them know you've taken care of the duplicate charge. Another option would be to adjust the next transaction date ahead one frequency so they won't be charged next time.
We sincerely apologize for confusion this has caused. Once we discovered what happened, we realized the chances of it happening as it did were about a tenth of a percent so this was a very obscure, unlikely issue. We're taking steps to ensure it can not happen again.