Another good one is http://gmvault.org. I used this just recently to backup and transfer all of my Google Apps emails to a separate gmail account since I'm transferring my apps domain to a different provider. Going just off of what the article says about BaGoMa, Gmvault seems to be comparable in features.
From a quick glance Gmvault looks preferable from a security standpoint as your credentials get saved in ~/.gmvault rather than being passed as a command-line argument, which could be viewed by any user on the system.
Been trying to get gmvault to do at least one successful run since it showed up on HN maybe a week or so ago. It always stops somewhere at mails from 2008 with no error message, just dies. Guess I'll wait until it's a bit more mature. I only have 6GB of mails too.
Gmvault can fail for multiple reasons, for example Gmail can cut the connection and throttle you for a while.
There are also bugs left or GMail emails that cannot be downloaded (email corruption ?).
For this reason, there is a --restart option for the sync and restore mode (sync being the backup).
The restart mode is a resume mode that will restart the backup or restore near from where it failed.
With that mode you should be able to download your 6 GB on disk.
