Due to winter break, I had not updated my Archlinux install for about a month. During that time, there appeared to have been several major changes, including a kernel update as well as an Xorg update.
When I rebooted, I found that my multi-monitor setup was borked. It was doing a very bad job of mirroring the displays when I wanted them to be extended.
It turns out that the Xorg update changed the reference names for the monitors. VGA and LVDS are now VGA1 and LVDS1, respectively. A bit of playing around with xrandr in the command line solved that nicely, though I admit I was in a panic and ready to ask the forums for advice.
