The next time you receive a Word, Excel, or PowerPoint document as an attachment in Gmail, hover over the attachment card with your mouse. You should see a pencil icon alongside options to download the document or save it to Google Drive. Click the pencil icon and a new tab opens, where you can edit a copy of the document that has automatically been converted to Google's Docs format.
Why this matters: One of the biggest stumbling block for Google Drive adoption has always been that Microsoft's Office formats are the default choice for most of the working world. To overcome that, Google needs to make it dead easy for Drive users to work with and manipulate Office documents. One-click editing in Gmail is something users have long needed to make editing documents more seamless inside Google's ecosystem.
More formats
In addition to making it easier to edit Office documents from Gmail, Google made another 15 Office formats compatible with Google Drive. The most important additions to the list being PPS and PPSX PowerPoint files, as well as DOCM and XLSM formats.
If converting an Office document to Google Docs format is a non-starter, Google also offers a Chrome extension that lets you edit an office document in its original format.
Once the extension is installed, click on the name of the file in Gmail, and then in the tab that opens click Open at the top of the screen. The document will then be ready for editing without conversion.
If you don't see the pencil icon in Gmail yet, it will likely roll out to your account in the coming days. In my tests, the new feature was only available for free accounts, and not yet added to Google Apps for paying users.