I'm getting the same behavior that's been mentioned here (on one of my WordPress blogs; on the other one AWB is working splendidly). That is, all the requirements are OK and green, and when I click "save changes and backup," it goes through all the steps with no errors and when I reload the settings page, as it instructs me to do after the backup 'finishes,' there is no backup listed, and the Amazon bucket is still empty.
The sites are on bluehost.
I'm also using these plugins, which I've tried disabling one-by-one, with no success: Custom Query String, Google Analyticator, reCAPTCHA, Wordbook, and WP-Footnotes; the theme is Neoclassical 1.1.
The one thing I notice is that in the wp-content/uploads/awb directory, there is an error_log file, with entries like this:
[15-Jan-2011 20:15:35] PHP Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 42991894 bytes) in /home/username/public_html/weblog/wp-content/plugins/automatic-wordpress-backup/automatic-wordpress-backup.php on line 1100
And I don't really know enough php to do anything with that.