I've tried what you all recommended--cleaning the sensor, setting the speed to super low, increasing stitch length, BSR2 (I always used that one anyway). While perhaps
slightly improved, it's still looking pretty terrible, and definitely a lot worse than my old-fashioned free-motion quilting. What is strange is that my mom has an Aurora 440QE with the BSR, and I tried it over the holidays and it acted pretty much the same way, which would suggest either user error or a whole batch of bad BSRs. I will contact Bernina, and perhaps drop by the dealer I've been buying feet from in the hopes that they'll take pity on me if I act pathetic since I'll be in the area next week.
Again, thank you all so much for your help!
@sewingsuz: it's supposed to move continuously. I think it's so that you can take securing stitches at the beginning and end of a line of quilting.