It's been a long time coming (and I haven't yet seen an official announcement by Google) but IMAP is now supported in GMail and I can now change the way I handle backing up of my GMail account (and back up everything that I received/sent before implementing the forward-to-backup implenentation).

If you don't believe me, see the "Forwarding and POP/IMAP" tab now available in GMail's settings.