Firstly, I was trying to work out why, half way through a scene, my mist stopped seeping, rolling and doing what mist generally does and instead just hung in mid air. While I'd set the simulation to run through the whole scene, baking had only been set up for the first 250 frames. D'oh! (Particles, like water, have to be baked before you can use them. Obviously.)
Secondly I've been fighting a running battle with Blender's chroma keying system. Admittedly I started off with not the greatest quality footage. Problem solved by chaining large numbers of keying nodes together, each set to spot a slightly different shade of green, but the resulting noodle network is reaching a scary level of complexity: I won't be handing over control of the world's defence systems to it any time soon. And that's before I add the blurs, glows etc. The cat version of TRON may not be released for another few months...
Finally, I'm now conditioned to using right click instead of left to select - which means I constantly try to use right click to select things in Windows as well.
I wonder if Hot Chip suffered from the same kind of difficulties with chroma key while filming this pop video. Enjoy! (embedding disabled - sorry)