WordPress MU

Is there some hook to know a new blog is created?

I see the following in the wpmu_create_blog function:

do_action( 'wpmu_new_blog', $blog_id, $user_id );

do_action is the hooks, right?

hello experts,

I am using this function however i am noticing that the user_id is not getting passed? Why would that be ? Am I not defining my function properly?
my action handler prototype is

"function ne_blog_signup_sync($blog_id, $user_id)"

but the user_id variable is coming up blank.

nevermind. I figured it out. I need to pass more parameters to the "add_action" call