Finally! OMG! Booyah! Oh, Vey!
You can now save attachments directly to Drive from within Gmail messages.
Rolling out to Google Apps for Business, Government, and Education over the next week or so, you no longer need to download to your desktop or “Downloads” folder and then sync or upload files in Drive.
From inside the message, you can preview or save files directly into drive, with the ability to browse and select folders.
Click here for more info and usage examples.