Alexandre,
We're looking into why those emails aren't going out right now. We changed some things around for the Joomla 2.5 release (to update to how Joomla sends those emails), and it seems like something isn't working right. They should be going out though *unless* you're using a JFBC Profiles plugin for CB. In that case, we instruct CB to send out the registration emails.
This problem is something we're looking into for the 4.2.2 release (likely coming out next week).
Alex