yesterday I updated my WordPress-Installation to 3.4 and a couple plugins (including Contact Form 7 to Database Extension) as well. After this update all my data "vanished".
I looked into phpmyadmin and found the table with all my data, but the plugin doesn't detect it and I noticed a oddity in the naming of the cf7dbplugin_submits table. I use a table prefix with approximately this pattern 'abcXYZ_'. All tables use *exactly* this prefix, only the cf7dbplugin_submits table was named "abcxyz_cf7dbplugin_submits" (all lowercase). After renaming the table to abcXYZ_cf7dbplugin_submits all data entries were back.
The plugin used to work fine before. Because I won't be able to verify this bug before Saturday I decided to report this now.