Google Mail in a nutshell:
1) Items land in your inbox
2) You make a choice (Delete or Archive)
3) Apply labels to help you find the item later (if you want)..
Google Mail is not about Folders. It is about Labels.
The Tragic Flaw with Folders:
Use this feature to ...
Labels offer the ability to describe an item in multiple ways
You can star items, set them as tasks, answer forms, generate calendar events, embed other documents, and tag content directly in Google Mail.
Google Mail will instantly find you any item you want, based on the label you ask for.
You can even save favorite searches as labels.
Google Mail will automatically label incoming messages, based on rules you set up.
This is like putting an item in a folder, but it means that you can train Google Mail to put any item that comes to you in the future in the same folder. Future folder stuffing, that's the powert of Google Mail.
BTW, Google images identifies this as an automatic stamping machine. Who knew?