Ran another test today--I smoked 4 racks of ribs on my UDS with the controller. (Which I'm calling the UDS Digital Supervisor, or UDS. Yeah, bad joke.) The supervisor worked very well; here's the chart:
What you might notice is that ~40 minutes into the cook the pit temperature (red line) plummeted 50 degrees. I freaked out at the time but I think what happened was that the wind changed and was blowing away the heat on the top rack (which is near the seal between the top of the drum and the lid). The thermometer on the bottom rack (light-blue line) didn't drop and then went up as the fan kicked in. It wasn't until 12:00 that I figured this out and put up a wind screen next to the smoker--you can see the two thermometers begin to converge after that.
The supervisor kept the pit temp very near the target temp for over 6 hours. The craziness at the end is when I opened the smoker to pull out the ribs but forgot to turn off the supervisor.