The problem is that what you are doing is putting your trust in a service over which you have no control. Your data is on a remote server, and when it all goes wrong... well, what can you do?
Earlier this week Google's popular GMail was hit by an outage. This is not the first time Google has had problems with their services. There was the famous case of the dissapearing iGoogle pages and email (as with any email service) does come and go. The most frustrating thing with an online provider is that you don't really know where to go to find out what is going on, if anyone knows it is broken, and if the are going to fix it. Well Google users need worry no longer. Google have used their Apps Status Dashboard which means that when your Google service isn't working you can see what is going on.