talking about integrating phpbb3 users to joomla.
I’ve tried JFUSION and darn its the worst module I have ever used (its so messed up and complicated more than expected)
I’ve tried to find another and hopelessly, I found nothing that can help me to do that COMPLICATED job (being sarcastic if you havnt figured that yet) honestly I was starting to make one on my own but wait wait there is a great one out there called rokbridge, or ROKBRIDGE.
And yes its the best it creates a non-invasive bridge solution for the fantastic new phpBB3 forum package.
you can check it here :

http://www.rocketwerx.com/products/rokbridge/