Having just lost all 3G connectivity to my Pre. I have become painfully aware of another suggestion - Automatic Backup of the Checkbook data.
Since adding the backup when exiting goes against the flow of throwing the card off the screen and ending the program. You could add the backup to the beginning of the program. You could add options to the Preferences Screen to capture the Google Docs info and to capture the Users desired backup frequency (Automatically Backup Checkbook every X times the program is started).
If you don't want to force a backup, at least throw up a reminder screen. For example:
You haven't backed up Checkbook in the last X days. Do you want to Backup Now?
You have been in the Checkbook program x times without a Backup. Do you want to Backup Now?
Forturately I have a secure WiFi Hotspot at home, so I was able to Backup Checkbook using it. But next time I might be so lucky.