I just upgraded Joomla to 2.5 (started back in the Mambo days). When the site came back online and the first user registered through JFBC, an admin mail got sent to 6000 regular users! Very bad for my reputation and I had a lot of angry mails to answer
I assume the sendEmail field in the jos_users table was used for something else in the past. For an unknown reason, some 6000 of my user accounts had it set to 1. This could have been avoided if JFBC would respect the mail_to_admin parameter of com_users, which I have set to 0.
I'm generally happy with JFBC, but this was a really bad experience, so I wanted to let you all know. Until SC checks the mail_to_admin parameter, all people who do a Joomla upgrade should better double check the values of sendEmail field in the user table.