I've never seen any (official at least) Alfresco mailing lists, my guess would be that forums are where discussions mainly take place. I know that there's an Alfresco user group on LinkedIn and probably also on Facebook, but I don't know how active they are.
In my opinion the discussions here are pretty active, but it could be better, but one guess might be that this is partly due to the fact that Alfresco is a rather commercial open source product. The Alfresco employees and many partners do a great job here (and in the wiki), but I sometimes feel that there is a lack of a really active user base on the grass root level.
