I'm also interested in this feature!
I have a user group VIP's and a forum called VIP-Lounge and I want to put users automatically in this group, when they reach a certain post count. I will do that with the mod "auto groups".
But it's also important to inform users about their new access rights! A private message would be better than an email, that will eventually not be read by the user before he comes back to the forum. Second, I need different notifications for each group. I think that is not possible with the mod "Email To User On Group Status Change".
I am already using the welcom pm mod: http://www.phpbb.com/community/viewtopi ... it=rank+pm
It's basically the same feature, only that pm's will be send on first login instead of a specific post count.