You are running a business. You don't want downtime, you want your email to be as reliable as the sunrise. Google Apps has been adjusting their service level agreements over the years to accommodate to the high demands of the millions of businesses that use their productivity software each day.
Before we talk about that though, I wanted to share an announcement Google recently had. In 2010, the Gmail email service, which provides both free consumer and business email services globally, was available 99.984% of the time. That means about seven minutes of downtime per month on average was experienced in 2010. According to Google, the seven minute average comes from a lot of tiny delays that normally consisted of a few seconds a shot. Most users experienced no issues, and in the rare case they did, a few seconds of delay is pretty easy to miss.