I found a great tool for backing up your Gmail account onto your own hard disk. You can also use it to restore your emails so you can merge Gmail accounts, etc.
I like Gmail, I use it for my personal and work email, but I have always kept a copy of all emails myself on my desktop computer. There are horror stories online of people losing their Gmail account and I just want to play safe. After all, it is a free service and Google can’t be expected to be fully liable if anything goes wrong.