Absolutely. When a user registers using Facebook, their Facebook email address will be used in the Joomla user manager. Do note, that when the user registers and 'approves' the Facebook Application, they are given the option to provide a 'proxy' email address instead of their real address. The proxy email address still goes to the user, but first passes through Facebook's servers for some quick spam checks. Primarily, Facebook ensures that the sending domain is from the same as your application.
In our experience, over 90% of users leave the (default) option of "real email" address set. Your mileage of course, may vary.
If you want to test the email capture abilities, you can do so on this site, which creates the user automatically and uses the Facebook email address. Alternatively, you can try our demo site, below, which lets the user choose a username and their email address.
Hope this helps! If you have any other questions, let us know.
Email addresses
