I've recently noticed that Google now offers 2 step auth to login to the Google Account and therefore Gmail, Calendar, Google Doc etc, this provides an additional layer of security when signing in.
Instead of using login/password only, you need to enter a verification code in addition, just like you need for some online banking. But instead of a security device, you can use your phone (iPhone, Android, Blackberry), iPod or a normal phone via SMS or voice message. If you use the iPhone/iPod app, you don't even need to be online to generate the verification code.
How it works - Accounts Help
If you have some apps accessing your Google account (ie. Outlook, or Gmail on your phone), you can setup application specific passwords that work for that purpose only).
Sounds a bit complicated, but if you have a lot of stuff on your Google Account you may want to look into this option. If this has been around for a long time, then I apologize for the dust.