Gmail went down at 2.PM IST yesterday affecting as many as 110 million users worldwide. You can imagine how many people are using their service and how badly they might get affected because of a few hours of disruption.
It is believed that this was the result of several thousands of computers operated by a few people hitting the gmail servers continuously for a few seconds.
It is said that Google has service level agreements with corporates to provide 99.9% gmail availability time in a month and with yesterday's disruption it already was down for 0.44% time in this month. With no other service provider meeting the pace and standards set by Google, I don't think corporates would take this glitch as a serious issue.