I posted my theory yesterday on why SharePoint discussion lists aren't used more. The votes are in and it looks like I am out-gunned on this one with most folks blaming poor feature set for low take-up.
So let's flip the discussion around and ask what new features are required to make discussion lists viable? My biggest complaint is that we have too many ways of doing discussions with little/no integration between them. There are email distribution lists, Exchange public folders, SharePoint discussions. Then going outside the firewall we have usenet groups, various types of web-based discussion board etc. Seems to me like this is exactly the sort of thing Pat Helland is talking about when he evangelises Metropolis and Jack Greenfield when he discusses Software Factories. If there were some kind of standardised interface to all these discussion platforms then it wouldn't matter which one I was using. I'd just use my favourite discussion viewer app to connect to them all, kinda like we all use our favourite RSS Reader to connect to blogs and sites running on lots of different software and hardware platforms. That would work for me anyway...what would work for you?
[Update 17 March 05]
Just come across an interesting piece of freeware: Macaw discussion board for SharePoint - looks like it addresses many of the issues raised in the comments here.