How do pci-e extenders, seen in this topic: https://forum.bitcoin.org/index.php?topic=6128.0 work? Can someone post a picture of a mining rig that uses those extenders? I'm having a hard time picturing how they could be useful, because the card will be more or less dangling from the cable.

Obviously you have to screw the card into something, or lay it on something, or support it in some way shape or form. An extender for PCIE is just like an extender for anything else. It simply frees you from the confines of shoving cards directly into PCIE slots in the way the motherboard is laid out.

If for example you had a motherboard with 2 PCI-E slots that were stupidly placed right next to each other (meaning 2 2-slot cards would be impossible to fit) you could use an extender for the second PCI-E slot and simply screw the card in a few slots farther down on your case. Or build a custom case. The sky is the limit.

I saw that picture, but it looked like all the video cards were plugged in.