Using it on Joomla 2.5.4 and IPB 3.2.3.
When you create a account with IPB, you can then also login to joomla with this username & password.
When looking in the user-table of joomla (administrator) you can see that if a user exist in IPB the user will be added as a registered member. (after a successful login).
Good work Dev.
Maybe some more functions?