Hi! Wow, I can't believe I was asking these questions only a year ago. I went with a 100+ node DMX based RS485 setup. It worked beautifully.
Apollo 13: Mission Control | Flickr.
I adapted code from Max Piersons's blog:
http://blog.wingedvictorydesign.com/2009/03/20/receive-dmx-512-with-an-arduino/
and designed my own boards. I have not, as yet, embarked on each node transmitting (although this is definitely still on the cards). The next stage is to use LED drivers to extend the number of LED's. Control is from a LanBox. I can give a more detailed description of the system later... If there is interest? r