Nice orginazation. I've got a collection about as big as Eilif's maybe even large, but only about a third of it is sorted, since I've had it even since I was 3 and never even thought about sorting until I got involved online.
What I am planning to do is first sort 85% (the rest is for friends who are visiting and want to build with a random box) by color, and after that's all done, go separating them by size. I would separate them by piece type, but I don't have enough space or containers.
Right now about 1/3 of my collection is sorted by color. I've also got a bunch of "tiny boxes", all filled with pieces smaller than a 1x2 brick. I've also got a minifig box, an animal box, a couple of tackle boxes with greebles, clips, printed tiles, turntables, bedy pieces, and things like that in them, and also a bunch of binders full of instruction booklets organized by theme. My next step is to keep dumping out random boxes and sorting them by color, while removing useful pieces and other stuff.
I envy your amount of space, Eilif. Good luck to your sorting.