VGA over Cat5 ethernet cable

That would definitely be pretty awesome if this works. At work I have a blackbox vga/keyboard/mouse over cat5 adapter, but it's rather expensive and is more than just a connector. This would be great for in wall touchscreens.
On the linked page, it talks about getting ghosting or smearing with an 800x600 display over 50 feet of cable. This is definitely a try-it-and-see kind of application.

There is nothing special about this. You can use any wire to extend a vga signal. Pick up some Romex or extension chords at HomeDepot and have at it - all it's got to do is conduct electricity. Just about any wire you use will cause image degradation just because of the length. I don't think there are any real properties in cat5 that make it work much better than anything else - the twist is probably not sufficient and its effects may vary greatly depending on which lines are twisted together.