Official Google Blog: What we learned from 1 million businesses in the cloud
googleblog.blogspot.com
googleblog.blogspot.com
Actually, I bet the email outages are some of the most productive time in a company :)
In fact, I may propose a pseudo-Victorian movement for Natural Productivity. Motto yet to be determined, actually, natch.
Can you trust a another company like Google or Amazon with your personal/private data or your company or client's sensitive data?
If you are just using error rates from the requests that make it to the application then it seems this measure of reliability doesn't account for a lot of infrastructure at Google (ie, load balancers, switches, etc). Service interruptions and downtime with infrastructure like this should definitely be accounted for by a measure of reliability for Gmail since the end-user needs all of it to work to use the app.
One solution could be factoring in some sort of availability monitor at the border of Google's networks that polls/uses the Gmail service like an end-user.