It's a cool concept and as a CSS fan, I had toyed with the idea for my own forum until time stopped me even trying. Good job.
BTW, FluxBB and it's cousin, PunBB are pure CSS. I nearly chose them as my forum software of choice, but ultimately MyBB was more developed and had more features out-of-the-box and won.
It's not really THAT fluid, btw.....