Read post, then watch video.
Thank you, everyone, for the supportive wishes and good cheer! I hope to be back blogging properly tomorrow, but in the meantime, go read Aprilynne Pike's That Was MY Idea! post. Short summary: it doesn't matter if the idea's been done before, it's all about how you execute it. Okay, now you can watch the video.
ETA: Here's a perfect example. I just saw a Twitter #pubtip from Rachelle Gardener that said: I can't think of a more over-used plot device in kids/YA fiction than the "magical portal." So, just because Lewis Carroll and C.S. Lewis did it, should Neil Gaiman not have bothered to write Coraline? Yes, lots of books include a door to another world. How will YOU write it?