Am I backing up WordPress adequately?

Hi all,

I just want to make sure that I’m backing up my wordpress blog sufficiently. I use wordpress database backup plugin by Austin Matzko (http://austinmatzko.com/wordpress-plugins/wp-db-backup/) to send an automatic backup to my email address each day.

In addition to this I use the same plugin to do a manual backup save to my hard drive every so often.

Is this sufficient or is it foolish to rely on one plugin?

Thank you,
Jason.