Hi Alex,
I'm using JFBConnect in automatic mode and I already found where the accounts are created... unfortunately for me you indeed do invoke $user->save() (or Store()... I don't remember exactly) and that indeed tiggers all user-related events

... so that breaks my theory. Anyway I should say that the bridge is working just perfect out of the box - they provide an option to create phpbb3 users in almost any situations but here's what happens:
- a person from Facebook creates new account on my web site using JFBConnect
- upon that registration no phpbb3 user is created by the bridge but that's basically ok most of the time
- when the same user actually logs-in into my web site (using FB credentials of course) the bridge is able to create new phpbb3 account (that's optional synchronization in p8pbb... and almost all bridges support the same functionality). So the phpbb3 user is created on log-in and not on registration
- If a returning Facebook user comes back to my web site with modified e-mail, user name or password (.. whatever) you identify him/her by some tokens and it's correctly mapped to Joomla but (for example) his e-mail needs to be modified both in Joomla and phpbb3 databases... and here comes the problem - if p8pbb plug-ins are not triggered on user-related actions I just cannot be sure what's going on and sooner or later I'll end up with a lot of out-of-sync user details in phpbb3... It could be even worst - I'm not sure if p8pbb would not create new phpbb3 account for each returning FB user with modified details (for example if I have an account john. smith and later the same user comes back with new name, say marry.popins, I'm not sure if your component wouldn't update john. smith to marry.popins... if it does so then according to p8pbb rules (or any other bridge) that's actually a new registration and they would create new account in phpbb3's database. What should happen in the same situation is: you update john.smith to marry.popins, some bridge's event is triggered, the bridge updates also phpbb3 database and everyone is happy (including me)... It's easier for me to debug user's registration and that's why I'm trying to make it work without all optional synchronizations (by default p8pbb is creating new phpbb3 account on Joomla registration and they have an optional synchronization later on login to create phpbb3 user if username is not found in phpbb3)
Some of this explanation is just a theory - I'm not sure if you update Joomla account's details for returning users with modified data and if you do so what exactly could be altered... if you never change user names all bridges should be happy but that's not very user friendly. I'm still waiting for any response from Blogomunity and I keep digging into source codes to check other theories... It was very useful for me to understand that you're actually using user tokens to create a map between FB users and Joomla.
Please do not waste your time on this subject - I have your source codes and I can answer most of my questions by looking at them. I created this topic in case you already had the same issues before and you have some solutions ready to go. I consider my problem much beyond the scope of a normal support - your component alone is working just perfect and actually all of my problems are coming from the bridge itself... I just want to make my web site registrations rock-solid for additional custom scenarios. It's a bit difficult for me to explain what I want in English and my explanations are a bit messy - sorry for that
Regards
EDIT: If someone is interested in this topic I should say that p8pbb developers actually found an issue in their component and it's fixed now. Both plugins are working toghether without any custom modifications and for all possible scenarios (just make sure that p8pbb is the last one in plugins order).