First a general point: I doubt that mimicking the client to that level of detail is the most useful model here. The good thing about a web-based interface is that you have the freedom to adopt it to what best suits the medium and the anticipated use. Compare any professional software that is available on different platforms and on different devices and you'll see that every local implementation wields the strengths of the respective medium.

With that in mind, consider the following: the logic of the client (an entire row is a link) is adapted to the reality of the three-pane design of the local client. A click on the row brings up metadata on the right while the item list remains in sight. The web doesn't work like that: people are used to opening things in new tabs and expect different linked pieces of information to lead to different places. And especially when the pieces are not only informationally different but also visually presented as distinct, it runs counter good UI design practices to point them to the same place.

Regarding the more specific points:

#1:

I'd be happy to hear what other people who are using groups to collaborate more extensively than I am think and I'll be happy to be overruled

What are your sources for getting this kind of information and when do you allow yourself to be overruled? Considering that we know that the bulk of users won't speak their mind here on the forums, it seems important to have reliable ways of identifying how people work with the Groups web interface. I am reporting not just for myself by the way but also for colleagues who have expressed some mystification about that page and generally avoid it.

Also, the fact that you're torn by it doesn't mean that if you include both, they should look the same (as they do now). I have often noticed that the web interface is very underspecified when it comes to distinguishing types of information that are in fact very different both conceptually and in the way users handle them. That contributes to the feeling of "underdesignedness". But anyway, my position is that only top-level items should be listed on this home-page. A separate way to keep track of recent "notes" activity would be cool, but I think "notes" activity and "recently added items" are two very distinct things worth keeping separate.

#2, #4: Why a linked "added by", which identifies a user account, should ever be anything else than a link to that user's profile, is mysterious to me.

#3: Well, anything that's easy to get is already an improvement. Right now the page is underdesigned and not information-rich -- very much unexpected for a page that is the number one place where users end up when they (1) double-click group name in their library or (2) search for groups. Right now sending them straight to the library would be more useful (I see people doing that all the time, indicating that the homepage is experienced as a stumbling block rather than a helpful first stop).

#5: Great!

The library view is designed to be a single page web app, as browsing an entire Zotero library of any significant size is not particularly suited to more classical web patterns. This has the downside of sometimes breaking expectations (though expectations are rapidly changing) but the alternatives are fairly untenable.

The logic of the website library is the same as that of the client. Clicking a row brings up the full metadata for that item. In most cases it should happen nearly instantaneously. The table doesn't stay in view, but it maintains its state (and the page keeps all the library data it has loaded). The styling of the table is also intended to indicate that the entire row of data is the clickable element. The only reason the text is linked at all is semantic. You have brought to my attention that usernames are not linked to profiles in the item details, which I think was just an oversight on my part and will be fixed.

Note that this doesn't apply to the usernames on the recently added listing. I only said it was the same as the library interface to explain the current state, not argue that it needed to stay that way.

The idea of separating notes activity is interesting, but I'm not sure yet what that might look like in a way that accomodates the many different ways people use notes. It may be that a simple list of most recently modified notes (with indication of parents?) would be sufficient.

In any case, the group page is definitely less useful (and uglier, as it was not given as much attention as it deserves during the last redesign) than it could be. If you have more ideas for what you would find useful on there please do throw more suggestions out and we can see about how feasible they are.