POW!
this is the semi-result (its not quite finished yet) of some of my research into occlusion culling.
screenshot:
link to demo: (click the big red button to toggle the magic)
http://dev.bwhiting.co.uk/b3d/occlusion/
the big red planes are marked as occluders and are semi-transparent so you can see what is going on behind em 😉
If you want to know more about this just let me know, have half written 2 posts about the inner workings of this but lack motivation to finish them.