We got an interesting tip from "Jack", who noted that you could affect the time remaining on an iTunes movie rental by altering your system time. I gave it a shot to be sure. It's true, if you're willing to offset the date on your computer until you finally have time to watch that movie, you can get past the 30-day time limit.
It was also noted that if you fast-forward your calendar to the due date of a rental, iTunes will remove the movie from the library but apparently not from your drive. That seems odd to me, but that's the way it works, at least if you switch the date up yourself. And sure, you could get a little creative with a DVR and some streaming output, but the price isn't so bad to me that it warrants the extra effort. My movie-watching habits seem to be in line with Apple's plan: I generally watch a movie once no matter how good it is. Ultimately, it's just a matter of finding the time to do it.