Yes SpiNNaker looks very cool, also of course the BBC Micro connection as you say. I do wonder what the network architecture is, so now I'm going to have to watch that video you posted :-)

Edit: It's a toroid, which seems an unusual choice (because 2D) for something that's meant to simulate a brain. I wonder if a simple 3D cubic connection network would have been possible by adding more links between physically adjacent boards.