After upgrading to the most recent version [2.2.3], on a multisite installation (4 blogs), suddenly the plugin stopped sending the daily backup emails.
I just went in to the admin and ran two backups manually -- one to download, which was never downloaded (though it went to 100% and said was finished), and one to send via email (it completed and said the email was sent but I never received it).
The plugin has worked flawlessly for 2 years or so up until this upgrade. On single-site blogs, I don't have this problem... the plugin is still working fine after upgrading.
The db isn't too big -- 3megs...