I am a big advocate of Google and all their awesome FREE services, however with something as important as email you don't want to be at the mercy of Google. If you don't have a backup of your gmail account you will have nobody to blame but yourself.
Also, I think with the launch of Google +, doing regular backups of your gmail account is even more important than ever. Google is entering the social network sphere and all of us with Google accounts are part of that social network. Now where you can get into trouble, is if Google suspends your account because of misuse. There have been some people that have had their accounts suspended due to violations of the user terms. Most of these people were probably spammers, but you never know, something you might do will have Google's robots turning the suspension switch on for your account. Imagine losing all of your data you have amassed over the years. So here are a few ways to backup your data.