I was playing with Windows Azure durable virtual machines. In the end, I deleted the virtual machine (successfully) and tried to delete the associated storage account.
Unfortunately there is the case where the VM was deleted but Disks shows the VM attached to the blob (a 30GB VHD) precluding the deletion. Also there is the case of using the Azure Storage Explorer you find an orfan but leased VHD blob that can't be deleted and there is no reference on the Preview Portal.