In a blog post, Microsoft says this about the new Google Drive support for Outlook.com
First, begin a new message and then click or tap the attachment icon. Next, select Google Drive and enter your account credentials. Once added, your Google Drive appears as a source when attaching files. You can browse and select your files from either a list view or as thumbnails. You could always edit Google file types with a shared link—but previously it would open the file in a new tab. Now, when you receive a Google Doc, Slide or Sheet, you can open the file within Outlook
Here's how Outlook.com users can add their Facebook photos:
The steps for connecting a Facebook account are the same as with Google Drive—simply click or tap the attachment icon from within a new message and enter your credentials. Once connected, you'll be able to browse and attach your photos. Your photos will be organized just like they are in Facebook: "Photos of me" are the ones that you've been tagged in and "My photos" are the ones you've uploaded.
Finally, Microsoft has made finding a specific attachment easier in a long email conversation on Outlook.com:
At the top of every thread, you'll now find an attachment icon. Click it to open a drop-down list of all the attachments in the conversation. Simply select the file you are looking for and open it—you don't have to click though each reply or expand the thread.
These new features are being rolled out to all Outlook.com users over the next few weeks.