The customer service manager at Zip.ca told me they were changing some procedures, and service would soon improve. It did.
Whether the improved service was coincidental to my complaint, or a function of it, I don't know. But since I complained, we've been receiving our top priority movies, even after I added many titles back on our ZipList.
The race was on to see which would come first, "The Departed" and "Borat" DVDs, or baseball season. We just mailed back "The Departed," and Zip says that "Borat" is on the way. Yay!
I'll actually be out of town for the first two weeks of baseball season, so my first real games will be the Red Sox here in Toronto. Double yay!