For past 30+ minutes, Gmail is not responding and the request die with 502 Server Error.
Update: Gmail blog reports that outages occured due to “we took a small fraction of Gmail's servers offline to perform routine upgrades in the morning (Pacific Time), and later on a few of the request routers became overloaded and in effect told the rest of the system "stop sending us traffic, we're too slow!". This transferred the load onto the remaining request routers, causing a few more of them to also become overloaded, and within minutes nearly all of the request routers were overloaded. As a result, people couldn't access Gmail via the web interface because their requests couldn't be routed to a Gmail server. IMAP/POP access and mail processing continued to work normally because these requests don't use the same routers.”