Great. Just a couple of points off the top:
1) Authentication really appears to need some work. When I try to reply to posts I usually end up having to relogin. Then on older posts (for example, tried to reply to this: http://www.silverstripe.com/general-discussion/flat/486), it appears that I can reply but then it asks for login info and then even after entering my correct credentials it would not actually go on into reply but rather kept displaying the login form. Either the post is not able to be replied to any longer or there is an error of some sort. Either way it is not being handled in a clear way.
2) Profile management could be in a more prominent place. Login and forgotten password reset options should also be in more prominent places. It just needs a good usability and UI overhaul. Obviously this is theme related, but needed.
3) You may wish to do some more in the way of threading and the way that posts are displayed as well as have a section in the profile for showing threads to which you are subscribed as well as threads of which you are a part or parent.
I'm sure I could think of more as well, but we'll leave it at those for the moment.
Also, I am trying to figure out how to add simple authentication for groups as per Sigurd's notes earlier that I'd pasted above. Not put much effort in yet, but is there anything yet clearly documented for this? I'd love to see a quick example of this that works as I've got a quick urgent need and very little time (read no time :\ ) to plug it into a system for a quick solution.
