Looks like Microsoft has made available the very first update to Office 2013 Customer Preview. Office 2013 was made available to the public as a Customer Preview on the 16th of July and this update should bring some stability and bug fixes.
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Stay tuned as we try to attain an official change log. With any update, it is safe to assume that this update brings stability enhancements as well as bug fixes to the Customer Preview build of Office 2013. More on this as it develops.