***UPDATE, 5:40 PM ET***
GMail appears to be back up and running and Google says the problem should be resolved.
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Google says its email service is suffering a major disruption impacting the "majority" of its users. When GMail is down, you can go to Google's App Status Dashboard to check on the status of the application.
For more streaming updates, check out the Twitter module directly below.
The New York Times' Gadgetwise blog has additional details on the current outage.
And not that anyone needed proof of how integral and essential GMail is to so many people's lives, but this screengrab from Google Trends really drives the point home: