1) I would like to see an option in my profile to have e-mail notification standard checked (or not if you choose to) whenever I post a new topic.
2) Another great feature would be to have e-mail notification of topics that you didn't start, but participate in.
3) Even greater

would be to have an option to subscribe to topics that you don't participate in. An option to unsubscribe would be another plus.
4) Another option would be to select when and how you want the e-mails to be sent. One message per topic? Or one message for all topics of that day? One message per topic until the next visit?