I was going to say definitely subfolders, but do you mean sort of like a spreadsheet?
This image shows the subfolders which you can collapse and expand in the project panel. But I guess it isn't what you were looking for.
<img src="http://dl.dropbox.com/u/57899112/subfolders.PNG" border="0" />
As far as subfolders go, it would be nice if you could:
1) click on subfolder name to select all of the instances of the objects in the folder.
2) drag and drop the subfolder to the layout to create an instance of each object in the subfolder.
But better BY FAR would be hierarchical grouped objects. You could do so much with them!