While the main point of this article is about legislation that enables interception, they're using gmail as an example and there's something I'd like to point out (took a little digging to find a place where this had been said publicly):
http://googleblog.blogspot.co.uk/2014/03/staying-at-forefron...
"In addition, every single email message you send or receive—100 percent of them—is encrypted while moving internally. This ensures that your messages are safe not only when they move between you and Gmail's servers, but also as they move between Google's data centers—something we made a top priority after last summer’s revelations."
The NSA can lawfully intercept all of Google's inter-datacenter traffic at the borders of the US. Good luck to them in doing anything useful with this firehose of encrypted traffic.