1. Decide what you want to get out of it - There are many different levels of listening.  If you can decide what you want to accomplish ahead of time, you can choose an appropriate way to listen.  For example, if you just want a survey of the course material or to brush up on a topic with which you are already familar, you might be able to listen while doing chores around the house.  If you want to deeply understand a new complex field, you might not be able to listen while doing the laundry.

2. Ask questions -  Just because it isn’t an actual class, doesn’t mean you can’t ask questions.  If you don’t understand something, say your question outloud or write it down.  Better yet pause the podcast and try to find the answer on Google.  By asking questions you’ll engage your mind in a deeper way.  This will make up for some of the distractions that you will face by not being in an actual class.

3. Look for inconsistencies - On of the commenters on Digg was listening to on of the podcasts and thought he caught a professor in a contradiction.  The professor cleared it up in the next sentence.  By looking carefully for inconsistencies, you will keep you mind engaged with the material–who knows you may actually find an error as well.

4. Take notes - This can be done on many levels.  Just simply jotting down the 5 most interesting points after listening to a lecture will help solidify what you’ve learned.  It doesn’t have to be a long drawn out process, you just need to make a few notes about what caught your attention.

5. Review your notes -  If you have a list of the 5 top points from any lecture, spending a few minutes to review them each day will help remind you of what you’ve learned.  The best way to remember something is through repeated exposure over time.  Reviewing your top 5 list for each lecture is a simple way to do this.

6. Talk to someone else about the content - One of the most valuable parts of a classroom is having other students around for discussions.  You can simulate this by getting together a group of people who want to learn the same thing.  The discussions don’t have to be long and drawn out.  For example, if you and your co-worker listen to the same lecture on the way to work and have a 5 minute discussion each morning, your ability to assimilate the information will be dramatically better than just listening by yourself. If there isn’t anyone who wants to listen to the same lecture, you could find someone who wouldn’t mind you explaining to them what you’ve learned. Even blogging about interesting points can be beneficial.  It is just a matter of having to explain the content to someone else.

7. Interact with the content any way possible - Any thing you can get your mind to interact with the content will give your mind more of an opportunity to assimilate what you’ve learned. Even simple things like browsing the books on the topic at a local bookstore, making contributions to the Wikipedia entry on the subject, participating in a mailing list on a related topic, and participating in a related forum make a big difference in your ability to retain and comprehend new information. One idea might be to sketch a rough concept map while you are listening. Another useful way to add visiual pep to teh audio stream is to Google a term using the Images filter - this will give you many visual cues about the topic.