I didn't even know they existed. =]

My favorite "network thing I didn't know existed until recently" was the two-way splitters. Something we'd been wiring here by hand for a long time and is available as a simple plug-in dealie.

A cat-5 cable has eight wires. Only four of those wires are used for ordinary LAN communication.

So if you want, you can put one of these "splitters" on one end of a cable run (say, the single port at a guy's desk) and put another splitter at the other end of the cable run (say, just before the hub) and you get two network plugs for the price of one.

You still need two ports on the hub, what you're saving is a second cable-run.

Dunno how well it works for 100 megabit, but we've been using it successfully for 10 megabit for years now.