David,
An automatic update notification is a good idea, I guess, for many users. Making the functionality optional for sure is needed. Not everybody would like this (me for example).
When you notify a new release on the forum, the

new post indicator and the

indicator are very helpfull to see where to go on the forum.
Alternative idea : Registered users can subscribe for e-mail noticifation for a new-release-announcement. You don't need any automatic feedback from our computers. You know you have a new release and for sure, nobody has that new release at release-moment. Thus you can do an email-blast without feedback what release I am using.
Regards,
Sander