CB 2.0 will mark the completion of the refactoring which is currently well underway in soon to be released CB 1.2, and which will continue with CB 1.3.

This will position CB 2.0 as a cross-platforms native users-management framework, with many integrations-possibilities, thanks to its API and framework.

CB 1.3 will unveil as users-features some of the big improvements made "under the hood" of CB 1.2, while CB 2.0 will hopefully show the true power of the power-engine which is taking shape

I don't want to promise here any magic solution, but just say that it is one of the main goals of CB 2.0 to be able to manage natively users across sites. We hope to achieve that goal next year.

That said there are a few solutions to do such synchronizations today, mostly commercial. I didn't try them and can't comment on any so far.

You also have a few plugins for CB which allow you to synchronize joomla with forums, and such plugins exist for Joomla too.

CB 1.2 RC 4 introduces the possibility to use such Joomla 1.5 authentication plugins (or to develop CB authentication plugins as well !), which could allow for community- or third-party provided synchronization solution already with CB 1.2 Stable, as a CB plugin.

So...looking forward to some really exciting stuff ahead