Update 3, 4:30pm: Google says things are back to normal now:
Your chats are back. We've resolved today's issues with Hangouts and Talk—thanks for your patience. goo.gl/mhHhmM—
A Googler (@google) March 17, 2014
Update 2: Google Docs and Sheets are also down for some users.
Update: Google is investigating issues with Hangouts and Google Talk:
Google’s chat services through the Hangouts apps on mobile, inside Gmail and elsewhere are currently experience outages for a growing number users. Google is yet to update its app status page to reflect the issues but we’ve reached out to the company about the problem and we’ll update when we know more.