The Geography of You and Me, by Jennifer E. Smith

The night the lights go out all over the Northeast, Lucy and Owen find themselves stuck in a stalled elevator in their Manhattan apartment.  Once rescued, they decide to spend the evening together.  The city -- without electricity -- has become magical, a surprisingly friendly town where you can even see the stars from Central Park.

Afterwards, they move on -- Owen and his father move out west, while Lucy and her parents relocate to Edinburgh and then to London.  Long distance relationships are hard (especially when you're not really sure what the nature of the relationship is in the first place), but the friendship born that night survives and they stay in touch through postcards and occasional emails.

I loved the characters (so full of hope and anxiety).  I loved the settings (so many familiar places from New York to Seattle to Edinburgh, and just enough detail to make them seem authentic without overdoing things).  But most of all, I loved the sheer beauty of the story -- a simple romance to be sure, but a captivating one based on honesty and believability.  I might have gotten a bit annoyed towards the end when Smith drags everything out a bit more, but I forgave her as soon as I got to the pay-off.