Just because Google wants you to put your digital life in the cloud doesn't mean you can't have your own copy of your own messages and attachments. There’re lots of ways to get your entire Gmail dump onto your desktop. We're currently into Gmail Backup, which is graphical for Windows and command line for Linux and Mac OS X. You can also grab it with the command-line-based Fetchmail, grab them via POP with Thunderbird, or use the web-based StashMyMail for 99 cents, if you don't mind the third-party-ness of it. To back up another email account using Gmail's generous storage space, you can always BCC: your outgoing messages to a Gmail account to make sure you've always got an online searchable copy of your mail.