How safe is our data in the cloud? This is a question that all cloud users and non-users have asked. Google has addressed this in a recent blog post that gets into some of the fine details of the data backup process. If a Google data center is disrupted/destroyed, Google's backup system is set up such that no data should be lost (Recovery Point Objective) and the time without access to Google Apps services is zero (Recovery Time Objective). They achieve this with high speed simultaneous replication of Google Apps user's actions at two data centers; and this is done for the major apps in Google's Apps suite: Calendar, Sites, Docs, and Gmail.
This is great to know since we are investing so much more time in the cloud. Hopefully the other cloud vendors will release information on their backup procedures to ensure that their customers feel safe using their product.
Note: As an extra security measure, I export my documents to one of my hard drives, it's a "just-in-case" thing.