So everything's working fine. Nearly
Things like raspivid -o video.h264 works fine which I can play elsewhere no problem. But when I stream netcat I get problems.
I think it's raspivid not working when I don't have an output file. If I run raspivid -o - then I get the preview for about 5 seconds then the machine either hangs, or I get loads of strange characters on the screen. If I clear the screen and type anything it looks like a strange character mapping. Weird behaviour I can emulate always. Tried it on two pis. Tried different power supplies too. Different images. Etc Etc. now run out of ideas