Having Google handle your organization’s security does bring many benefits to your IT department. Since no server or software upkeep is necessary, all updates and security fixes are handled on Google’s side. For in-house content regulation, Google Apps administrators have the power to restrict access to their domain’s online services. Google provides domain settings where the admin control panel can prevent any document or calendar sharing outside the organization. This is especially useful with Google Docs where a large number of collaborators may need to edit a very secure document. Turning on the domain security settings can keep your organization’s vital information from being compromised.

Google's security isn't perfect, however: As of summer 2009 several security experts have noted that Gmail, Google docs and Google calendar are vulnerable to hijacking because they are not automatically encrypted (Security Fix, Top Security Minds Urge Google to Encrypt All Services, June 16, 2009). 

Users can avoid this problem in Gmail by turning on an option that permanently keeps their email encrypted.  A similar option is not available for Google docs and Google calendar, though users can access encrypted versions of these services by typing https://docs.google.com or https://www.google.com/calendar directly into their browser's location bar.

Links
http://googleonlinesecurity.blogspot.com/