I run a similar site to Ian, and every so often we have an offer from someone to message all our users with a newsletter.
Unfortunately each time I have to decline as I don't want to send 10k emails to people, plus I think I should never send any ads to email boxes (plus many email addresses listed in users' profiles are out of date).
An internal PM solution would solve the issue as I would be able to send all my users a message without resorting to emails.
