I've been getting a bit carried away recently searching on youtube for videos that demonstrate the surgery. But don't worry, they're just computer images, not actual videos of the operations, so nothing gory!
The first one here shows what I now think I'll be having done. It's called a bimaxillary surgery (i.e. two jaw surgery). The operation on the bottom jaw elongates it (mandibular advancement) and the operation on the top jaw reduces the length of the jaw, to stop the smile looking so gummy and makes the face look less long (LeFort 1 operation). I read somewhere that this surgery takes about 5 hours to complete.
This next one shows just the lower jaw surgery...
And this one shows just the top jaw surgery. I don't think I'm anywhere near as gummy as this video shows, but it still illustrates the sugery well. It shows it in a bit more detail than the bimaxillary video...