I recently had the hair-raising experience of losing all my to-do items. Others have reported this, and I'm not blaming Toodledo. The cause was probably GotToDo on my Android phone, and Toododo's policy is to disclaim responsibility, which is their privilege.
I hereby request an automatic daily database backup of some kind. Even simply putting all deleted items (regardless of the source of the deletion request) into a "deleted" folder would be a big help. But I'm willing to be patient.
For the benefit of others, though, I'd like to tell how I recovered my data. As it happens, I had the Windows program TaskAngel running, with a regular sync setup. TaskAngel can be set to back up its database automatically! I simply opened the backup file, re-synched, and was restored to the date of the last backup. Some cleanup work required, but not much. The default location for TaskAngel data, including the backup file, is C:\Users\Dan\AppData\Roaming\MyPocketSoft\TaskAngel.