We have a working custom function on our BP site that does the following:
1. notifies all members of a Group when a
a. new topic is created
b. post occurs on a topic in the group
We are in the process of adding the capability of a user to control these settings as well. We will post the code when we are finished, unless of course, Andy beats us to it and then we’ll use his!
FYI – it dramatically increases forum participation