I followed instructions carefully and it worked first time. It is important to put the WP phpBB Bridge widget in your sidebar before activating the bridge (which is not the same thing as activating the plugin). The widget allows you log in and out. So it goes like this:
1. Activate plugin
2. Place widget in sidebar
3. Activate bridge
I REALLY like the fact that after users have logged in to the forum, they find they are automatically registered and logged in to my members only blog, so there's only one username/password for them to remember.
I would like the option to remove the link to the blog control panel. I don't want my users to have access to this.
ETA I managed to remove that link by editing wpbb_users_widget.php.
2nd ETA It's also working fine with WP 3.5