Things I've done with the time (which otherwise would have never happened):
-Used Pimsleur I-III to learn some Mandarin, and more importantly, HOW to learn a new language(/other things). Spoken Mandarin is less intimidating than westerners think, and the grammar is simpler than English in a lot of ways. (Caveat: My Mandarin is by no means good. I couldn't find any good systematic ways to keep going after Pimsleur III)
-Listened to podcasts on nutrition and got very in-tune with how what I eat effects how I feel, how productive I am, and what happens during my gym time.
-Neuroscience podcasts, ditto. That stuff is interesting. Especially relating to dopamine, if you're a heavy internet user and you check your email every thirty seconds on your phone.
-Developed a better idea of how successful freelancers operate and how they've transitioned into that (Kalzumeus podcast, Ruby Freelancers). Ditto for very successful startup founders (Techzing, Stanford's Innovation Thought Leaders podcast).
-Developed my musical taste.
-Developed my rock climbing grip by using a grip trainer.
-Learned to calm my mind and relax and not waste mental energy on situations I have no immediate control over. Shitty traffic is a great time to practice this specifically because it's so aggravating.
That said - the key thing is that this is for a finite period of time, and you have to act on stuff you learn. The eventual endgame is that you gradually run out of interesting things that you can pick up from a podcast and then do on your own. You want to use the time to work on something more specific.
In addition to the time cost, sitting in one position and staring in one direction for an hour destroys any kind of flow that you have. It doesn't matter whether you leave work energized and ready to rock - when you get home, sitting in a car for an hour will usually make you tired. If you work on complex side projects or like to go out after work, this has a pretty substantial impact.