I haven’t seen a definitive list of WPMU actions like there is of WP Actions and WP Filters. So, while I don’t have diddly in the way of information for most of these, I’ll go ahead and give you the current list of actions that I’ve found. I’ve included what are my best guesses at the needed arguments, based on context:
add_user_to_blog($blog_id, $user_id, $role) /* Adds user to specified blog, assigns role remove_user_from_blog($user_id, $blog_id) /* Removes user from specified blog, does not delete wpmu_activate_user($user_id, $password, $meta)
wpmu_activate_blog($blog_id, $user_id, $password, $title, $meta)
Obviously, there’s not a lot to go on, here. But at least it gives you some idea of what actions are available and how to use them. The names are usually quite straight-forward and intuitive.
Do you know of any more? If you do, please share and I’ll update the list.