[toomuchtodo]

http://gmvault.org/

For those who can't code or don't have the time.

[pirer]

yep but you still need to know a few things as well as: https://github.com/abjennings/gmail-backup or http://www.fetchmail.info/ and https://github.com/Flushot/gmail-backup

[ams6110]

fetchmail for saving, notmuch for indexing/searching.

[blueblob]

offlineimap ftw.