When I arrived at the school they were using Paragon for cloning HDD's. This is done in a lab and physically booting each computer to CD and then accessing the image off of a external HDD via USB. I use CloneZilla and have my images on the server, which is in turn accessed from the pc via a bootable cd. Once I boot, I locate the image, and then pull it across the network. My images average 20-40Gb depending on class, and when I clone 12 @once and it takes about 20-30 minutes. I have cloned 30 @ once, but I usually start those and go home. They tend to take a bit longer.
I am currently researching the FOG project, and am attending a workshop on FOG here this spring. With FOG one can push images, updates, software installs and more. I don't have enough information on FOG yet to leave an informed post.