Offer a way to download all messages older than x days to a local computer and make them searchable (i.e. using Google Desktop Search).
This would be a way to clean up disk space while keeping older e-mails. 1 GB is smaller than we may think!
And another one (March 29th):
Include a download-feature so I can burn my old e-mails on CDROM.
If you want that feature too, please let Google know!