Hey,
I think it would be a good idea if, for new users, the email notification option was enabled by default.
It's happened to most of us: We've signed up to a forum, posted a question, then completely forgot about it.
If you're lucky, weeks/months later you remember about it, go and check it and it's got loads of replies. If only you'd known...
Some new users post a question and never go back to it, which, for the person who put their time and effort into trying to help them, is a complete waste of time.
So I think it'd be satisfying for the person helping to know that the user will be notified about the reply.
And of course it'd be helpful for the user to know someone's posted a reply to their topic.
Many other forums do this and I think it'd be a good idea to have it here.
Chris