Technically I imagine it would be that the community admin UI is far superior than ours. Vadim's right in that the OpenACS paradigm is that the core (subsite, actually) manages this for all packages. In this sense it makes NO SENSE to port phpBB's admin features to our forums package, because that's the wrong place to do user and group admin stuff in our multi-package environnment.
Somik may not be aware of our community admin pages if he's just looked at the forums package, but if he were he'd see quickly that they suck :)
Fortunately Lars Pind has already committed to spending time working up an admin UI for OpenACS, and we already have one volunteer willing to help implement better admin UI for the toolkit. And we're going to be looking at migrating relevant admin UI bits and pieces from dotLRN to the main toolkit.
So things are going to be getting vastly better in this area the next few months.
As far as 50 themes ... I'd love to see people start making available different skins for the toolkit. Mostly to demonstrate to folks that it's easy to do. The place to do that, though, is the subsite level not the forums level. We aren't quite 100% there regarding consistent use of CSS but we're talking about it for 4.7.
In fact it probably wouldn't be that hard to swipe phpBB's themes and recast them for OpenACS subsites if anyone thinks they're attractive enough to bother with.
Somik ... visit https://openacs.org/projects/dotlrn/
This is just a subsite mounted under openacs.org that has a different skin than the main openacs.org site. It's a very simple skin - really just the header is being skinned in this case - but that should give you the general idea, i.e. that you can mount a new subsite and give it a different skin. You also control user membership and all that at the subsite level. If you mount a forums package under a subsite like the dotLRN subsite it automatically inherits the skin for that subsite.
So this is where the effort goes ... making subsites better, not writing an individual package that has its own theming etc etc.
