Audio books have been becoming more and more prevalent recently than ever before, and it seems like they will not slow down anytime soon.
CDs and cassettes are becoming more and more obscure, and downloadable audio books are becoming more popular due to their ease of used and readiness online.  Not only that, but they are much cheaper than the hardcopy and CD forms.  This year more than ever, people will be using their MP3 players and computers to play their audio books rather than CD players and tape decks, because of the new advances in MP3 player technology.  Not only can you store and listen to hundreds of audio books on the go with a MP3 player like the iPod, but you can now play them in your car as well, all at your convenience.
Another great new thing about audio books is that, like CDs and hardcopy books, you can now rent audio books for a certain amount of time for a much cheaper price, instead of paying full price and buying them.
Online audio book services are also becoming more numbered recently.  They act a lot like a Rhapsody type music service, where you pay monthly fees and have unlimited access to all of the audio books that you would want.
So go ahead and get some audio books and see how convenient and useful they can be.  Whether it be commuting to work or exercising, they are a great new technology that you should take advantage of.