Apple has taken a step forward with iCloud, updating the beta to include co-editing capabilities. For each document that is shared, you can see the list of others with access to the document (“Collaborator List’) and the color-coded cursors of others editing the doc at the same time as you (‘Collaborator Cursor’). Also, Keynote, Numbers, and Pages docs can be placed in folders, but still are segregated, meaning you can’t have a folder with both Pages and Keynote docs, which is dumb.
Here’s a screenshot of a document collaborators list, with the color coding matching the cursors in the doc.
What is really essential is some way to converse about documents with others, and I favor comment threads outside the document, and perhaps one in each folder as well, especially once they clean up the dumb folder setup they now have.