Mismatch between bookmark-new and user-bookmarks
bookmark-new looks like a bookmark with a +, but user-bookmarks is a star - the metaphors don't match. This is why, when I did the Document Viewer mockups, I ended up drawing a new bookmark icon, to match bookmark-new.
We could decide that bookmarks should always look like stars. Or we could decide that it's worth having icons for both stars and bookmarks.