The following is a mail I posted on Magnolia-dev - why I prefer mailinglists over forums
we have thought about this (note: i.e. Forums). The main reason we do not like forums is that email is right there, always with you, whereas you have to visit a site to work the forum.
If it is just for archives, we can provide these.
However, we are open to discussion on issues like this, and as a matter of fact could set up a forum in less than a minute if people would really prefer that.
Personally, while this might seem old-fashioned, I love the fact that I have e.g. 30'000 emails from the webobjects developer list right here cached and indexed in my mail client, always with me wherever I go. Its a huge knowledge store, and its faster than any forum plus I do not need to be online to find an answer.
Also, you have options like digest and index if you just want to reduce the daily mail doses, you can filter to your heart's content ( I have rules that copy certain mails to certain subfolders within my mailing lists) etc.
All in all I believe you have more control, faster access and faster response times with a mailing list than with a forum, and I do not really see any advantages by using a forum other than archives, which we can provide as well.
To have both (mailing list and forum) seamlessly integrated would be sweet. However, in Java, I have only seen one open source solution that tries that, and decided not to integrate it into Magnolia (which of course would be the ultimate goal). To have such a tool for Magnolia would be great, not the least because it would store content in JCR, and this will give you a lot of nice options to retrieve that content, once level 2 functionality (e.g. arbitrary search; versioning) will be there.