My first exposure to this film was during the Oscars in 2007, where a grand-old spectacle was made out of Enchanted, whose songs owned 4 out of the 5 nominations for Best Original Song. Amy Adams and the rest of the cast rolled out like it was the fucking Tony Awards, performing their medley of Disney stuff and leaving to a standing ovation.
The stage turned, and he final nomination was a low-key, beautiful performance set to minimal staging -- just some guitars hanging, a grand piano, and two amazing musicians.
If you want a heart-warming Oscar moment (where John Travolta doesn't fuck up anyone's name), search "Falling Slowly Wins Best Song". From Glen Hansard's humble "Make Art!" speech to Marketa Irglova being brought back out by Jon Stewart after her speech was cut off, then delivering the best one of the night.
All of this on just a $100,000 budget, with the intention being just to pass the DVD out after concerts. This is probably my favorite song ever. You hear about movie magic -- here you have two non-actors, just truthfully and fully doing what they do, just learning a song... and it's beautiful. It's amazing what you can do with a small budget and a whole-lotta heart.
I've lived with musicians for the past two years. Before that, I was never really privy to the rehearsal process in music. It really is a wonderful thing. This scene is a perfect example.
"Once" is about as simple a plot as they come -- two lonely people meet, share a common love for music, collaborate, fall in love, make an album, she chooses someone else, he buys her a piano (actually, fuck, on second thought... it ain't THAT simple.) But it executes every musical sequence without doing anything fancy, and gets honest, raw performances out of its non-actors. And the music, oh man, the music...