How long is your commute? 2 minutes (to the home office), or an hour in a carpool in an HOV lane? Regardless of the duration, this is an opportunity for growth and development. Think of yourself as a captive audience.
I'm not sure how well you can pound out the next American novel on a laptop in a moving vehicle (looking at you, John Grisham), but writing while moving is something I cannot do. Reading is touch-and-go, depending on the pilot of the vehicle and the mode of transport. Plane? Great. Vehicle? Nope.
Living now in rural Wyoming and doing consulting work, it's clear I do quite a bit of driving. So in my case, neither reading nor writing are options. Recently, I joined Audible.com, a service now through Amazon, to listen to some of the books I had on my wishlist. I thought it would be a good way to make the most of long driving distances. Instead, I found it frustrating to drag through 18 hours of listening to a book I could read in 6. I know that there are variable speed settings, but these didn't seem to help my plight.
So, my preferred personal development tactic while driving is to listen to podcasts, Wyoming Public Radio (which is a fantastic service throughout the state), or TEDTalks. What are your commuting education pleasures?