I automatically end up in a collection “Synced Documents” (Synced via iDisk with Notebooks on my iPhone), and I’ve not yet figured out how to get out of that collection and back to my binder view. I checked the NaNo S2 help and while it describes collections, I did not see this. Thanks in advance!
Look right down at the bottom. If you have a collection selected, then just at the right hand edge of the binder/collections pane where it meets the left bottom corner of the editor pane you should see a little X in a circle. Click this to go to the binder view within the collections tab, or alternatively just click ‘Binder’ in the collections tabs (it’s usually just under ’ -Search Results- '). Once you have the binder tree shown within the collections, click the ‘Collections’ icon up above on the toolbar to get back to the standard binder view.
Eddy
The Binder tab is under the search results tab. Until you play with the colors, the binder almost disappears under the Search Results tab. Just click on it.
See picture.
Apollo16
Both of these responses are accurate. If the collection tab interface is hidden, the X button is your best bet. It will always be there and whenever your binder has a header title that doesn’t say “Binder” or is coloured differently, you should see the close button in the bottom-left corner of it. If the tabs are open, then clicking the big “Binder” tab is probably going to be easiest. 
Thanks, all! The fact that the “Binder” was grayed out kept me from clicking it.