Welp, my refurb 360 is actually not great. I hadn't used it for more than 10 minutes other than to rip discs and test out the disc drive.
Used it last night for a few hours, and after about 60-90 minutes, the display starts to get a horizontal split at the bottom of the screen that slowly creeps up. I thought it was a problem with the game I was playing, but it was on the dashboard too. Rebooting made it go away, and then it came back again within 90 minutes or so. Still haven't received my rebate, so I may just try to return or exchange.
Why do people take such bad care of their stuff? I know the 360 hardware was a little more fragile than other consoles, but the number of busted, dysfunctional systems that are out there now make it actually pretty hard to find a reliable system now.