I have friends who do this with lectures and audiobooks, which seems at least more productive-sounding.
I started with audiobooks and lectures as well. Since I'm a big fan of watching TV/Movies, applying the same thing to this area has allowed me to double the amount of consumption, while not really diminishing my enjoyment of the shows that I watch (and, in some cases, enhancing it if the show is slow but otherwise good).
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.