Comment 12 for bug 353126

I also get this problem using VirtualBox's display drivers (see https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/333564 which looks like a duplicate bug): if I am running a VM with desktop effects, I get no updates in vnc, but if I turn desktop effects off, everything returns to normal.

So it seems to be both nvidia and VirtualBox drivers that exhibit this problem. It isn't a problem on another laptop running 3d effects with an ATI card.