I have a few friends that have some pretty large message boards. I recently asked one of them to send an email to all registered memebers for something. Well my goal was acomplished because it served the intended purpose, but it also had an after affect.
The unintentional benefit was that members that have been dead, or non active for a long time, became active again.
I do not know if you do that or not, but it seems to have been a great way to draw a lot of inactive members back to a more active staus.