99.99 percent = 365 days x 24 hours x 0.01% = 0.876 hrs/year downtime = 52 minutes and 34 seconds.
"On Tuesday, Google Apps' Gmail service suffered significant availability problems that began in the morning (U.S. Eastern Time) and were declared officially solved for all users early Wednesday afternoon"
Quite a bit more than 52 minutes and 34 seconds of downtime. One might ask what promising 99.99% availability and failing so miserably does to the view on the web as an application platform. The availability might very well be the akilles heel for web 2.0 apps. For certain tasks there might be a tolerance for downtime. But, even simple productivity tools such as word processors are often critical tools in an enterprise.
By the way, Google Calendar is a nice app. But totally unreliable.