Designing a delete confirmation system

There are two ways to accidentally delete something, hitting the wrong key accidentally, and mistakenly thinking you are deleting the correct item. To avoid the first problem of accidentally hitting a key most systems require that you hit two keys in order to delete something. For instance in MS windows to delete a file you commomly hit the delete key and then are prompted with a confirm dialog. On a Mac they cleverly combine a two key combination (Command + delete) to delete a file. This avoids having to use a confirm dialog but is initially very frustrating for users that don't know the combination. Yahoo's mail interface also makes you hit two keys, first you have to select a checkbox from the list of emails, and then you click a delete button. All of these systems require that you do two actions to minimize the odds of accidentally deleting an item.

The other scenario is that you mistakenly think you should delete something and later realize it was a mistake. In this case a confirmation is unlikely to do any good since you may not realize your mistake till you need the file later. In that case all the systems mentioned have a "trash" system where you can retreive deleted items for days or weeks after they are deleted.