Depends on your goals.
If you are trying to encourage people to leave Yahoo Groups and come here, which believe me, we are, it has to have most if not all of the things that people used there.
A solid list server to me, sounds like a mailing list. Groups in Yahoo were so much more. They collected data, stored it on site, photos, files, databases, etc. they were our homes and they were bulldozed.
Mark's goal is to make it what people want, and make it a success. Therefore, listening to the ones from Yahoo who have either fled already or are about to, is to his benefit. The simple fact that so many people have clung to what is left of Yahoo Groups is testament to how badly we needed what was offered there.
And the reason we haven't left is it hasn't been offered anywhere else. Not one group site has EVERYTHING we lost in our Groups. Not one. But this one has that potential, and is well on the way to being somewhere people might actually migrate to. And Mark already has the key thing to making it a success.
Listening to and acting upon feedback by the users/beta testers, etc.
He certainly has that down, for sure.