Tried it, volume is too large. Every client I've tried crashes before it can get everything, and there is still the issue of convenient storage format. I'll probably have to write my own archiver.

I wrote this a few years ago to archive my Gmail emails to text files (and the attachments to whatever they are).

I haven't ran it in awhile but when I did it worked and was able to download my emails from the very beginning without crashing. Anyway, you might find it useful...

http://github.com/Jaymon/Popbak

I have been using Zimbra Desktop as an email client, http://www.zimbra.com/products/desktop.html, in my Mac in several GMail accounts with no problem. There are versions for Window and Linux.

So use getmail_fetch through the POP server; it downloads a few hundred at a time into a maildir format. Hard to get more convenient and storable than that (tar it up and gzip or 7zip it).