There's several things that impress me about these virtual choir performances, one of which is just pulling off the technical aspects of getting so many people together to do it. And of course there's the talent of the people involved. But I think what most impresses me is just the idea that people of diverse backgrounds got together just to create something of beauty.
Technical question: I assume many of the participants were using less than professional microphones and audio software in their homes. Wouldn't that affect how well they could all be in tune (not that to my ears there's any evidence they weren't)?