When you hover your mouse over an attachment in Gmail you will now be able to directly save the file to your Google Drive. In true Google-fashion, they have allowed you to customize the destination of the file by selecting which folder, or to create a folder within your Drive, that the file will land in.
Here is what it will look like when you hover over your attachment. All you have to do is click the Drive button:
IC's Devon Taylor created a phenomenal Youtube tutorial about this very feature. Take a few seconds and check it out: