Things I did not know about until recently: Ethernet splitters
Real cat-5 wiring, such as what they run through the walls of buildings, has eight wires; 100 Mbps and 10 Mbps Ethernet use four wires. If you have fixed cat-5 runs that you can't afford to add to, and you really need additional ports in places that already have one, and you can't afford to buy switches, you can take advantage of this to double up two Ethernet ports onto a single cat-5 run.
That's an Ethernet splitter. Ours look like slightly jumped up phone line splitters in industrial beige and are quite easily overlooked until the still innocent new person around the office wonders how two network cables seem to be coming out of one jack.
I was rather surprised; that you could do such perversities to cat-5 Ethernet had never occurred to me.
(When I saw the patch panel that is the other end was when the true horror started dawning, because of course you need one at each end. We are way, way over the wiring density our patch panels were designed for. (I have pictures, but I will spare my readers.))
Our one salvation may be that gigabit Ethernet needs all 8 wires, so if people want to move to gigabit they will have to be prepared to fund switches (or running more cat-5 wires in the walls). Unfortunately, I suspect that a lot of people around here will decide that gigabit is not really that important (for grad students) when they see the true costs.
(Ethernet splitters are not the same thing as Power over Ethernet splitters; the latter are an honorable and useful thing. Sometimes you can even run PoE over Ethernet splitters, resulting in the two sorts of splitters in sequence.)