Just can't figure out what it is good for, or what's the purpose. Maybe some video could help explain describing what it acctualy is. Still I don't know :)
Suppose your are a small game studio. You have a single profile card that describes your studio. Then you have a top level series for each of your games, say game A and game B. Then with the series for game A you can have sub series for Items, Characters, Locations. You then have cards that belong to each of those subseries featuring the items, characters, locations. Suppose there is a card for character x. That card can be updated with posts, every update has discussion forums... Best of all someone can quickly find all the characters in your game, all the locations and read information and discuss them.
Your point about a video is important. It has been considered but since there is considerable confusion about what this is for it seems wise to consider making one.
How is this different from a bookmark manager - or Evernote (which would display you some of the content in form of cards)?
I think the web site is probably more confusing than the app, especially if you're logged in the app and can view how to create cards.