Over the next few days, Google will be rolling out a new feature in BergApps that allows you to view email attachments and save them directly to your Google Drive without ever leaving the Gmail web client. When you view an email that contains an attachment, you'll see new preview tools at the bottom of the email as well as a new Drive button that lets you direct the attachment straight to your Google Drive space. Of course, you'll continue to be able to download and save the attachment to your local computer if you prefer.
This feature should begin rolling out to BergApps users the week of November 24, 2013. For more information, see Google's official blog post about this change.