Sending Email Updates to Users

Emails sent to Users [weekly by default?] to tell them what's going on.

Many users are not going to be in the habit of dropping around to the web site - so instead we must send them emails to tell them what's going on.

We need to be sensitive to their wants in terms of frequency of email, but at a base level we should occasionally tell them about stuff happening, and make it really easy for them to help us tune the content to their wishes.