In my previous post, I mentioned that my extrusion motor had conked out. The new one arrived, along with a new relay kit. I replaced the motor, and my Makerbot is printing again! (I didn't end up replacing the relay)
To test the new motor, I tried printing out an octocat and a handcrank for the z-axis. Both turned out well, so my next project is printing a spindle to hold my spool of plastic.