How do I close the editor in iPhoto?
Since I got different results from @Brandon, I started experimenting again. Esc, Done, and others behave as expected when I follow these steps:


Select Events from the Library group on the sidebar
Select your event
Edit a photo
Click done, press Esc, or any other quit-editing combination.
Voila, you're back at the event's thumbnail view.


If, however, you do as I've been doing while doing one-off imports of additional photos and merging them in to your existing event, you'll be in this situation:


Do work...
Select your event from the Recent group on the sidebar (first item under Recent, above "Last 12 months").
Edit a photo
Click done, press Esc, or any other quit-editing combination.
You're kicked back to the All events view, even though the sidebar shows your recent event is still selected.