The server was been down for almost 2 hours, according to Gmail blog it was server load problem. But according some friends it was been hacked by team of hackers. Confusing...
Take a look at this article which fully explains the downtime: http://gmailblog.blogspot.com/2009/09/more-on-todays-gmail-issue.html
Ohh...I didn't even noticed it. Its a serious fault on Google's behalf and they should make sure it doesn't happens again.
I've noticed some errors and run time error too but already fixed after couple of hours. Still Gmail did great job making things work sooner.